diff --git a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsConstructExpressionVisitor.java b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsConstructExpressionVisitor.java
index 4cfd42b55c7..6e2bd567fdf 100644
--- a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsConstructExpressionVisitor.java
+++ b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsConstructExpressionVisitor.java
@@ -5,6 +5,7 @@
 package com.google.dart.compiler.backend.js;
 
 import com.google.dart.compiler.backend.js.ast.*;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * Searches for method invocations in constructor expressions that would not
@@ -29,7 +30,7 @@ public class JsConstructExpressionVisitor extends RecursiveJsVisitor {
      * We only look at the array expression since the index has its own scope.
      */
     @Override
-    public void visitArrayAccess(JsArrayAccess x) {
+    public void visitArrayAccess(@NotNull JsArrayAccess x) {
         accept(x.getArrayExpression());
     }
 
@@ -37,23 +38,23 @@ public class JsConstructExpressionVisitor extends RecursiveJsVisitor {
      * Array literals have their own scoping.
      */
     @Override
-    public void visitArray(JsArrayLiteral x) {
+    public void visitArray(@NotNull JsArrayLiteral x) {
     }
 
     /**
      * Functions have their own scoping.
      */
     @Override
-    public void visitFunction(JsFunction x) {
+    public void visitFunction(@NotNull JsFunction x) {
     }
 
     @Override
-    public void visitInvocation(JsInvocation invocation) {
+    public void visitInvocation(@NotNull JsInvocation invocation) {
         containsInvocation = true;
     }
 
     @Override
-    public void visitNameRef(JsNameRef nameRef) {
+    public void visitNameRef(@NotNull JsNameRef nameRef) {
         if (!nameRef.isLeaf()) {
             accept(nameRef.getQualifier());
         }
@@ -63,14 +64,14 @@ public class JsConstructExpressionVisitor extends RecursiveJsVisitor {
      * New constructs bind to the nearest set of parentheses.
      */
     @Override
-    public void visitNew(JsNew x) {
+    public void visitNew(@NotNull JsNew x) {
     }
 
     /**
      * Object literals have their own scope.
      */
     @Override
-    public void visitObjectLiteral(JsObjectLiteral x) {
+    public void visitObjectLiteral(@NotNull JsObjectLiteral x) {
     }
 
     /**
diff --git a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsFirstExpressionVisitor.java b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsFirstExpressionVisitor.java
index 6789cd2bd71..633197db0aa 100644
--- a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsFirstExpressionVisitor.java
+++ b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsFirstExpressionVisitor.java
@@ -6,6 +6,7 @@ package com.google.dart.compiler.backend.js;
 
 import com.google.dart.compiler.backend.js.ast.*;
 import com.google.dart.compiler.backend.js.ast.JsExpressionStatement;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * Determines if an expression statement needs to be surrounded by parentheses.
@@ -49,56 +50,56 @@ public class JsFirstExpressionVisitor extends RecursiveJsVisitor {
     }
 
     @Override
-    public void visitArrayAccess(JsArrayAccess x) {
+    public void visitArrayAccess(@NotNull JsArrayAccess x) {
         accept(x.getArrayExpression());
     }
 
     @Override
-    public void visitArray(JsArrayLiteral x) {
+    public void visitArray(@NotNull JsArrayLiteral x) {
     }
 
     @Override
-    public void visitBinaryExpression(JsBinaryOperation x) {
+    public void visitBinaryExpression(@NotNull JsBinaryOperation x) {
         accept(x.getArg1());
     }
 
     @Override
-    public void visitConditional(JsConditional x) {
+    public void visitConditional(@NotNull JsConditional x) {
         accept(x.getTestExpression());
     }
 
     @Override
-    public void visitFunction(JsFunction x) {
+    public void visitFunction(@NotNull JsFunction x) {
         needsParentheses = true;
     }
 
     @Override
-    public void visitInvocation(JsInvocation invocation) {
+    public void visitInvocation(@NotNull JsInvocation invocation) {
         accept(invocation.getQualifier());
     }
 
     @Override
-    public void visitNameRef(JsNameRef nameRef) {
+    public void visitNameRef(@NotNull JsNameRef nameRef) {
         if (!nameRef.isLeaf()) {
             accept(nameRef.getQualifier());
         }
     }
 
     @Override
-    public void visitNew(JsNew x) {
+    public void visitNew(@NotNull JsNew x) {
     }
 
     @Override
-    public void visitObjectLiteral(JsObjectLiteral x) {
+    public void visitObjectLiteral(@NotNull JsObjectLiteral x) {
         needsParentheses = true;
     }
 
     @Override
-    public void visitPostfixOperation(JsPostfixOperation x) {
+    public void visitPostfixOperation(@NotNull JsPostfixOperation x) {
         accept(x.getArg());
     }
 
     @Override
-    public void visitPrefixOperation(JsPrefixOperation x) {
+    public void visitPrefixOperation(@NotNull JsPrefixOperation x) {
     }
 }
diff --git a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsPrecedenceVisitor.java b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsPrecedenceVisitor.java
index 3a2d8115da9..cf2c7f0d196 100644
--- a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsPrecedenceVisitor.java
+++ b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsPrecedenceVisitor.java
@@ -5,6 +5,7 @@
 package com.google.dart.compiler.backend.js;
 
 import com.google.dart.compiler.backend.js.ast.*;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * Precedence indices from "JavaScript - The Definitive Guide" 4th Edition (page
@@ -45,42 +46,42 @@ class JsPrecedenceVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitArrayAccess(JsArrayAccess x) {
+    public void visitArrayAccess(@NotNull JsArrayAccess x) {
         answer = 16;
     }
 
     @Override
-    public void visitArray(JsArrayLiteral x) {
+    public void visitArray(@NotNull JsArrayLiteral x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitBinaryExpression(JsBinaryOperation x) {
+    public void visitBinaryExpression(@NotNull JsBinaryOperation x) {
         answer = x.getOperator().getPrecedence();
     }
 
     @Override
-    public void visitBoolean(JsLiteral.JsBooleanLiteral x) {
+    public void visitBoolean(@NotNull JsLiteral.JsBooleanLiteral x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitConditional(JsConditional x) {
+    public void visitConditional(@NotNull JsConditional x) {
         answer = 3;
     }
 
     @Override
-    public void visitFunction(JsFunction x) {
+    public void visitFunction(@NotNull JsFunction x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitInvocation(JsInvocation invocation) {
+    public void visitInvocation(@NotNull JsInvocation invocation) {
         answer = 16;
     }
 
     @Override
-    public void visitNameRef(JsNameRef nameRef) {
+    public void visitNameRef(@NotNull JsNameRef nameRef) {
         if (nameRef.isLeaf()) {
             answer = 17; // primary
         }
@@ -90,62 +91,62 @@ class JsPrecedenceVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitNew(JsNew x) {
+    public void visitNew(@NotNull JsNew x) {
         answer = PRECEDENCE_NEW;
     }
 
     @Override
-    public void visitNull(JsNullLiteral x) {
+    public void visitNull(@NotNull JsNullLiteral x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitInt(JsNumberLiteral.JsIntLiteral x) {
+    public void visitInt(@NotNull JsNumberLiteral.JsIntLiteral x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitDouble(JsNumberLiteral.JsDoubleLiteral x) {
+    public void visitDouble(@NotNull JsNumberLiteral.JsDoubleLiteral x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitObjectLiteral(JsObjectLiteral x) {
+    public void visitObjectLiteral(@NotNull JsObjectLiteral x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitPostfixOperation(JsPostfixOperation x) {
+    public void visitPostfixOperation(@NotNull JsPostfixOperation x) {
         answer = x.getOperator().getPrecedence();
     }
 
     @Override
-    public void visitPrefixOperation(JsPrefixOperation x) {
+    public void visitPrefixOperation(@NotNull JsPrefixOperation x) {
         answer = x.getOperator().getPrecedence();
     }
 
     @Override
-    public void visitPropertyInitializer(JsPropertyInitializer x) {
+    public void visitPropertyInitializer(@NotNull JsPropertyInitializer x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitRegExp(JsRegExp x) {
+    public void visitRegExp(@NotNull JsRegExp x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitString(JsStringLiteral x) {
+    public void visitString(@NotNull JsStringLiteral x) {
         answer = 17; // primary
     }
 
     @Override
-    public void visitThis(JsLiteral.JsThisRef x) {
+    public void visitThis(@NotNull JsLiteral.JsThisRef x) {
         answer = 17; // primary
     }
 
     @Override
-    protected void visitElement(JsNode node) {
+    protected void visitElement(@NotNull JsNode node) {
         throw new RuntimeException("Only expressions have precedence.");
     }
 }
diff --git a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsRequiresSemiVisitor.java b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsRequiresSemiVisitor.java
index b5a13be9400..880cce0bb6c 100644
--- a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsRequiresSemiVisitor.java
+++ b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsRequiresSemiVisitor.java
@@ -5,6 +5,7 @@
 package com.google.dart.compiler.backend.js;
 
 import com.google.dart.compiler.backend.js.ast.*;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * Determines if a statement at the end of a block requires a semicolon.
@@ -34,21 +35,21 @@ public class JsRequiresSemiVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitFor(JsFor x) {
+    public void visitFor(@NotNull JsFor x) {
         if (x.getBody() instanceof JsEmpty) {
             needsSemicolon = true;
         }
     }
 
     @Override
-    public void visitForIn(JsForIn x) {
+    public void visitForIn(@NotNull JsForIn x) {
         if (x.getBody() instanceof JsEmpty) {
             needsSemicolon = true;
         }
     }
 
     @Override
-    public void visitIf(JsIf x) {
+    public void visitIf(@NotNull JsIf x) {
         JsStatement thenStmt = x.getThenStatement();
         JsStatement elseStmt = x.getElseStatement();
         JsStatement toCheck = thenStmt;
@@ -65,14 +66,14 @@ public class JsRequiresSemiVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitLabel(JsLabel x) {
+    public void visitLabel(@NotNull JsLabel x) {
         if (x.getStatement() instanceof JsEmpty) {
             needsSemicolon = true;
         }
     }
 
     @Override
-    public void visitWhile(JsWhile x) {
+    public void visitWhile(@NotNull JsWhile x) {
         if (x.getBody() instanceof JsEmpty) {
             needsSemicolon = true;
         }
diff --git a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsToStringGenerationVisitor.java b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsToStringGenerationVisitor.java
index a0c73d3e1dc..b0e3c33b992 100644
--- a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsToStringGenerationVisitor.java
+++ b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsToStringGenerationVisitor.java
@@ -8,6 +8,7 @@ import com.google.dart.compiler.backend.js.ast.*;
 import com.google.dart.compiler.backend.js.ast.JsVars.JsVar;
 import com.google.dart.compiler.util.TextOutput;
 import gnu.trove.THashSet;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.Iterator;
 import java.util.List;
@@ -200,7 +201,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitArrayAccess(JsArrayAccess x) {
+    public void visitArrayAccess(@NotNull JsArrayAccess x) {
         printPair(x, x.getArrayExpression());
         leftSquare();
         accept(x.getIndexExpression());
@@ -208,7 +209,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitArray(JsArrayLiteral x) {
+    public void visitArray(@NotNull JsArrayLiteral x) {
         leftSquare();
         printExpressions(x.getExpressions());
         rightSquare();
@@ -227,7 +228,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitBinaryExpression(JsBinaryOperation binaryOperation) {
+    public void visitBinaryExpression(@NotNull JsBinaryOperation binaryOperation) {
         JsBinaryOperator operator = binaryOperation.getOperator();
         JsExpression arg1 = binaryOperation.getArg1();
         boolean isExpressionEnclosed = parenPush(binaryOperation, arg1, !operator.isLeftAssociative());
@@ -272,12 +273,12 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitBlock(JsBlock x) {
+    public void visitBlock(@NotNull JsBlock x) {
         printJsBlock(x, true);
     }
 
     @Override
-    public void visitBoolean(JsLiteral.JsBooleanLiteral x) {
+    public void visitBoolean(@NotNull JsLiteral.JsBooleanLiteral x) {
         if (x.getValue()) {
             p.print(CHARS_TRUE);
         }
@@ -287,13 +288,13 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitBreak(JsBreak x) {
+    public void visitBreak(@NotNull JsBreak x) {
         p.print(CHARS_BREAK);
         continueOrBreakLabel(x);
     }
 
     @Override
-    public void visitContinue(JsContinue x) {
+    public void visitContinue(@NotNull JsContinue x) {
         p.print(CHARS_CONTINUE);
         continueOrBreakLabel(x);
     }
@@ -307,7 +308,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitCase(JsCase x) {
+    public void visitCase(@NotNull JsCase x) {
         p.print(CHARS_CASE);
         space();
         accept(x.getCaseExpression());
@@ -332,7 +333,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitCatch(JsCatch x) {
+    public void visitCatch(@NotNull JsCatch x) {
         spaceOpt();
         p.print(CHARS_CATCH);
         spaceOpt();
@@ -355,7 +356,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitConditional(JsConditional x) {
+    public void visitConditional(@NotNull JsConditional x) {
         // Associativity: for the then and else branches, it is safe to insert
         // another
         // ternary expression, but if the test expression is a ternary, it should
@@ -387,12 +388,12 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitDebugger(JsDebugger x) {
+    public void visitDebugger(@NotNull JsDebugger x) {
         p.print(CHARS_DEBUGGER);
     }
 
     @Override
-    public void visitDefault(JsDefault x) {
+    public void visitDefault(@NotNull JsDefault x) {
         p.print(CHARS_DEFAULT);
         _colon();
 
@@ -400,7 +401,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitWhile(JsWhile x) {
+    public void visitWhile(@NotNull JsWhile x) {
         _while();
         spaceOpt();
         leftParen();
@@ -412,7 +413,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitDoWhile(JsDoWhile x) {
+    public void visitDoWhile(@NotNull JsDoWhile x) {
         p.print(CHARS_DO);
         nestedPush(x.getBody());
         accept(x.getBody());
@@ -433,11 +434,11 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitEmpty(JsEmpty x) {
+    public void visitEmpty(@NotNull JsEmpty x) {
     }
 
     @Override
-    public void visitExpressionStatement(JsExpressionStatement x) {
+    public void visitExpressionStatement(@NotNull JsExpressionStatement x) {
         boolean surroundWithParentheses = JsFirstExpressionVisitor.exec(x);
         if (surroundWithParentheses) {
             leftParen();
@@ -449,7 +450,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitFor(JsFor x) {
+    public void visitFor(@NotNull JsFor x) {
         _for();
         spaceOpt();
         leftParen();
@@ -488,7 +489,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitForIn(JsForIn x) {
+    public void visitForIn(@NotNull JsForIn x) {
         _for();
         spaceOpt();
         leftParen();
@@ -523,7 +524,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitFunction(JsFunction x) {
+    public void visitFunction(@NotNull JsFunction x) {
         p.print(CHARS_FUNCTION);
         space();
         if (x.getName() != null) {
@@ -546,7 +547,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitIf(JsIf x) {
+    public void visitIf(@NotNull JsIf x) {
         _if();
         spaceOpt();
         leftParen();
@@ -585,7 +586,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitInvocation(JsInvocation invocation) {
+    public void visitInvocation(@NotNull JsInvocation invocation) {
         printPair(invocation, invocation.getQualifier());
 
         leftParen();
@@ -594,7 +595,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitLabel(JsLabel x) {
+    public void visitLabel(@NotNull JsLabel x) {
         nameOf(x);
         _colon();
         spaceOpt();
@@ -602,7 +603,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitNameRef(JsNameRef nameRef) {
+    public void visitNameRef(@NotNull JsNameRef nameRef) {
         JsExpression qualifier = nameRef.getQualifier();
         if (qualifier != null) {
             final boolean enclose;
@@ -633,7 +634,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitNew(JsNew x) {
+    public void visitNew(@NotNull JsNew x) {
         p.print(CHARS_NEW);
         space();
 
@@ -653,22 +654,22 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitNull(JsNullLiteral x) {
+    public void visitNull(@NotNull JsNullLiteral x) {
         p.print(CHARS_NULL);
     }
 
     @Override
-    public void visitInt(JsIntLiteral x) {
+    public void visitInt(@NotNull JsIntLiteral x) {
         p.print(x.value);
     }
 
     @Override
-    public void visitDouble(JsDoubleLiteral x) {
+    public void visitDouble(@NotNull JsDoubleLiteral x) {
         p.print(x.value);
     }
 
     @Override
-    public void visitObjectLiteral(JsObjectLiteral objectLiteral) {
+    public void visitObjectLiteral(@NotNull JsObjectLiteral objectLiteral) {
         p.print('{');
         if (objectLiteral.isMultiline()) {
             p.indentIn();
@@ -720,12 +721,12 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitParameter(JsParameter x) {
+    public void visitParameter(@NotNull JsParameter x) {
         nameOf(x);
     }
 
     @Override
-    public void visitPostfixOperation(JsPostfixOperation x) {
+    public void visitPostfixOperation(@NotNull JsPostfixOperation x) {
         JsUnaryOperator op = x.getOperator();
         JsExpression arg = x.getArg();
         // unary operators always associate correctly (I think)
@@ -734,7 +735,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitPrefixOperation(JsPrefixOperation x) {
+    public void visitPrefixOperation(@NotNull JsPrefixOperation x) {
         JsUnaryOperator op = x.getOperator();
         p.print(op.getSymbol());
         JsExpression arg = x.getArg();
@@ -746,17 +747,17 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitProgram(JsProgram x) {
+    public void visitProgram(@NotNull JsProgram x) {
         p.print("<JsProgram>");
     }
 
     @Override
-    public void visitProgramFragment(JsProgramFragment x) {
+    public void visitProgramFragment(@NotNull JsProgramFragment x) {
         p.print("<JsProgramFragment>");
     }
 
     @Override
-    public void visitRegExp(JsRegExp x) {
+    public void visitRegExp(@NotNull JsRegExp x) {
         slash();
         p.print(x.getPattern());
         slash();
@@ -767,7 +768,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitReturn(JsReturn x) {
+    public void visitReturn(@NotNull JsReturn x) {
         p.print(CHARS_RETURN);
         JsExpression expr = x.getExpression();
         if (expr != null) {
@@ -777,12 +778,12 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitString(JsStringLiteral x) {
+    public void visitString(@NotNull JsStringLiteral x) {
         p.print(javaScriptString(x.getValue()));
     }
 
     @Override
-    public void visit(JsSwitch x) {
+    public void visit(@NotNull JsSwitch x) {
         p.print(CHARS_SWITCH);
         spaceOpt();
         leftParen();
@@ -795,19 +796,19 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitThis(JsLiteral.JsThisRef x) {
+    public void visitThis(@NotNull JsLiteral.JsThisRef x) {
         p.print(CHARS_THIS);
     }
 
     @Override
-    public void visitThrow(JsThrow x) {
+    public void visitThrow(@NotNull JsThrow x) {
         p.print(CHARS_THROW);
         space();
         accept(x.getExpression());
     }
 
     @Override
-    public void visitTry(JsTry x) {
+    public void visitTry(@NotNull JsTry x) {
         p.print(CHARS_TRY);
         spaceOpt();
         accept(x.getTryBlock());
@@ -823,7 +824,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visit(JsVar var) {
+    public void visit(@NotNull JsVar var) {
         nameOf(var);
         JsExpression initExpr = var.getInitExpression();
         if (initExpr != null) {
@@ -839,7 +840,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitVars(JsVars vars) {
+    public void visitVars(@NotNull JsVars vars) {
         var();
         space();
         boolean sep = false;
@@ -860,7 +861,7 @@ public class JsToStringGenerationVisitor extends JsVisitor {
     }
 
     @Override
-    public void visitDocComment(JsDocComment comment) {
+    public void visitDocComment(@NotNull JsDocComment comment) {
         boolean asSingleLine = comment.getTags().size() == 1;
         if (!asSingleLine) {
             newlineOpt();
diff --git a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/JsVisitor.kt b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/JsVisitor.kt
index 93c2eebf47f..bb4fdc44439 100644
--- a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/JsVisitor.kt
+++ b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/JsVisitor.kt
@@ -7,8 +7,8 @@ package com.google.dart.compiler.backend.js.ast
 import com.google.dart.compiler.backend.js.ast.JsVars.JsVar
 
 public abstract class JsVisitor {
-    public open fun <T : JsNode> accept(node: T) {
-        node.accept(this)
+    public open fun <T : JsNode?> accept(node: T) {
+        node?.accept(this)
     }
 
     public fun <T : JsNode> acceptList(collection: List<T>) {
diff --git a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/RecursiveJsVisitor.java b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/RecursiveJsVisitor.java
index 56cb331b789..23f84dbd85f 100644
--- a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/RecursiveJsVisitor.java
+++ b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/RecursiveJsVisitor.java
@@ -1,8 +1,10 @@
 package com.google.dart.compiler.backend.js.ast;
 
+import org.jetbrains.annotations.NotNull;
+
 public abstract class RecursiveJsVisitor extends JsVisitor {
     @Override
-    protected void visitElement(JsNode node) {
+    protected void visitElement(@NotNull JsNode node) {
         node.acceptChildren(this);
     }
 }
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/InstanceCollector.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/InstanceCollector.kt
index e9362aacda7..d6f882b74ab 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/InstanceCollector.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/InstanceCollector.kt
@@ -23,7 +23,7 @@ import java.util.ArrayList
 class InstanceCollector<T : JsNode>(val klass: Class<T>) : RecursiveJsVisitor() {
     public val collected: MutableList<T> = ArrayList()
 
-    override fun visitElement(node: JsNode?) {
+    override fun visitElement(node: JsNode) {
         if (klass.isInstance(node)) {
             collected.add(klass.cast(node)!!)
         }
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/NameCollector.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/NameCollector.kt
index a13c5591062..6bb1f7a400f 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/NameCollector.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/NameCollector.kt
@@ -28,12 +28,12 @@ import java.util.HashMap
 class NameCollector(private val scope: JsScope) : RecursiveJsVisitor() {
     public val names: MutableMap<String, JsName> = HashMap()
 
-    override fun visit(x: JsVars.JsVar?) {
+    override fun visit(x: JsVars.JsVar) {
         super.visit(x)
         addNameIfNeeded(x)
     }
 
-    override fun visitFunction(x: JsFunction?) { }
+    override fun visitFunction(x: JsFunction) { }
 
     private fun addNameIfNeeded(hasName: HasName?) {
         val name = hasName?.getName()
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/PropertyCollector.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/PropertyCollector.kt
index b9f5bd6feac..664950f0108 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/PropertyCollector.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/PropertyCollector.kt
@@ -24,14 +24,14 @@ import java.util.IdentityHashMap
 class PropertyCollector : RecursiveJsVisitor() {
     public val properties: IdentityHashMap<JsName, JsExpression> = IdentityHashMap()
 
-    override fun visitPropertyInitializer(x: JsPropertyInitializer?) {
+    override fun visitPropertyInitializer(x: JsPropertyInitializer) {
         super.visitPropertyInitializer(x)
 
-        val label = x?.getLabelExpr() as? JsNameRef
+        val label = x.getLabelExpr() as? JsNameRef
         val name = label?.getName()
         if (name == null) return
 
-        val value = x?.getValueExpr()
+        val value = x.getValueExpr()
         properties[name] = value
     }
 }
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/sideEffectUtils.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/sideEffectUtils.kt
index fae7a17bc73..c79cab3746b 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/sideEffectUtils.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/sideEffectUtils.kt
@@ -46,7 +46,7 @@ private open class SideEffectVisitor() : RecursiveJsVisitor() {
     public var sideEffectFree: Boolean = true
         protected set
 
-    override fun visitElement(node: JsNode?) {
+    override fun visitElement(node: JsNode) {
         sideEffectFree = sideEffectFree && isSideEffectFree(node)
 
         if (sideEffectFree) {
@@ -54,7 +54,7 @@ private open class SideEffectVisitor() : RecursiveJsVisitor() {
         }
     }
 
-    protected open fun isSideEffectFree(node: JsNode?): Boolean =
+    protected open fun isSideEffectFree(node: JsNode): Boolean =
         when (node) {
             is JsValueLiteral,
             is JsConditional,
@@ -70,7 +70,7 @@ private open class SideEffectVisitor() : RecursiveJsVisitor() {
 }
 
 private class NeedToAliasVisitor() : SideEffectVisitor() {
-    override fun isSideEffectFree(node: JsNode?): Boolean =
+    override fun isSideEffectFree(node: JsNode): Boolean =
         when (node) {
             is JsThisRef,
             is JsConditional,
diff --git a/js/js.tests/test/org/jetbrains/kotlin/js/test/utils/CallCounter.java b/js/js.tests/test/org/jetbrains/kotlin/js/test/utils/CallCounter.java
index 0b181e175d2..9f88fc7152d 100644
--- a/js/js.tests/test/org/jetbrains/kotlin/js/test/utils/CallCounter.java
+++ b/js/js.tests/test/org/jetbrains/kotlin/js/test/utils/CallCounter.java
@@ -56,7 +56,7 @@ public class CallCounter extends RecursiveJsVisitor {
     }
 
     @Override
-    public void visitInvocation(JsInvocation invocation) {
+    public void visitInvocation(@NotNull JsInvocation invocation) {
         super.visitInvocation(invocation);
         JsExpression qualifier = invocation.getQualifier();
 
diff --git a/js/js.translator/src/org/jetbrains/kotlin/js/sourceMap/JsSourceGenerationVisitor.java b/js/js.translator/src/org/jetbrains/kotlin/js/sourceMap/JsSourceGenerationVisitor.java
index 3de2602e08f..cfc6969d3b4 100644
--- a/js/js.translator/src/org/jetbrains/kotlin/js/sourceMap/JsSourceGenerationVisitor.java
+++ b/js/js.translator/src/org/jetbrains/kotlin/js/sourceMap/JsSourceGenerationVisitor.java
@@ -20,6 +20,7 @@ import com.google.dart.compiler.backend.js.JsToStringGenerationVisitor;
 import com.google.dart.compiler.backend.js.ast.*;
 import com.google.dart.compiler.util.TextOutput;
 import com.intellij.util.SmartList;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.List;
@@ -37,7 +38,7 @@ public class JsSourceGenerationVisitor extends JsToStringGenerationVisitor imple
     }
 
     @Override
-    public void visitProgramFragment(JsProgramFragment x) {
+    public void visitProgramFragment(@NotNull JsProgramFragment x) {
         x.acceptChildren(this);
     }
 
@@ -87,7 +88,7 @@ public class JsSourceGenerationVisitor extends JsToStringGenerationVisitor imple
     }
 
     @Override
-    public void visitProgram(JsProgram program) {
+    public void visitProgram(@NotNull JsProgram program) {
         program.acceptChildren(this);
         if (sourceMapBuilder != null) {
             sourceMapBuilder.addLink();
diff --git a/js/js.translator/src/org/jetbrains/kotlin/js/translate/utils/inlineUtils.kt b/js/js.translator/src/org/jetbrains/kotlin/js/translate/utils/inlineUtils.kt
index 9793fd7d31f..22f57fc34e6 100644
--- a/js/js.translator/src/org/jetbrains/kotlin/js/translate/utils/inlineUtils.kt
+++ b/js/js.translator/src/org/jetbrains/kotlin/js/translate/utils/inlineUtils.kt
@@ -51,9 +51,7 @@ fun setInlineCallMetadata(
     val name = context.aliasedName(descriptor)
 
     val visitor = object : RecursiveJsVisitor() {
-        override fun visitInvocation(invocation: JsInvocation?) {
-            if (invocation == null) return
-
+        override fun visitInvocation(invocation: JsInvocation) {
             super.visitInvocation(invocation)
 
             if (name == invocation.name) {