diff --git a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/JsVisitorWithContext.java b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/JsVisitorWithContext.java
index 9d4224e686e..bd817120a65 100644
--- a/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/JsVisitorWithContext.java
+++ b/js/js.dart-ast/src/com/google/dart/compiler/backend/js/ast/JsVisitorWithContext.java
@@ -22,6 +22,8 @@ package com.google.dart.compiler.backend.js.ast;
  *  file: dev/core/src/com/google/gwt/dev/js/ast/JsVisitor.java
  */
 
+import org.jetbrains.annotations.NotNull;
+
 import java.util.List;
 
 /**
@@ -31,10 +33,14 @@ import java.util.List;
 public abstract class JsVisitorWithContext {
 
     public final <T extends JsNode> T accept(T node) {
+        if (node == null) return null;
+
         return doAccept(node);
     }
 
     public JsExpression acceptLvalue(JsExpression expr) {
+        if (expr == null) return null;
+
         return doAcceptLvalue(expr);
     }
 
@@ -43,6 +49,8 @@ public abstract class JsVisitorWithContext {
     }
 
     public final <T extends JsStatement> T acceptStatement(T statement) {
+        if (statement == null) return null;
+
         //noinspection unchecked
         return (T) doAcceptStatement(statement);
     }
@@ -51,304 +59,304 @@ public abstract class JsVisitorWithContext {
         doAcceptStatementList(statements);
     }
 
-    public void endVisit(JsArrayAccess x, JsContext ctx) {
+    public void endVisit(@NotNull JsArrayAccess x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsArrayLiteral x, JsContext ctx) {
+    public void endVisit(@NotNull JsArrayLiteral x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsBinaryOperation x, JsContext ctx) {
+    public void endVisit(@NotNull JsBinaryOperation x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsBlock x, JsContext ctx) {
+    public void endVisit(@NotNull JsBlock x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsLiteral.JsBooleanLiteral x, JsContext ctx) {
+    public void endVisit(@NotNull JsLiteral.JsBooleanLiteral x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsBreak x, JsContext ctx) {
+    public void endVisit(@NotNull JsBreak x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsCase x, JsContext ctx) {
+    public void endVisit(@NotNull JsCase x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsCatch x, JsContext ctx) {
+    public void endVisit(@NotNull JsCatch x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsConditional x, JsContext ctx) {
+    public void endVisit(@NotNull JsConditional x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsContinue x, JsContext ctx) {
+    public void endVisit(@NotNull JsContinue x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsDebugger x, JsContext ctx) {
+    public void endVisit(@NotNull JsDebugger x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsDefault x, JsContext ctx) {
+    public void endVisit(@NotNull JsDefault x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsDoWhile x, JsContext ctx) {
+    public void endVisit(@NotNull JsDoWhile x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsEmpty x, JsContext ctx) {
+    public void endVisit(@NotNull JsEmpty x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsExpressionStatement x, JsContext ctx) {
+    public void endVisit(@NotNull JsExpressionStatement x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsFor x, JsContext ctx) {
+    public void endVisit(@NotNull JsFor x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsForIn x, JsContext ctx) {
+    public void endVisit(@NotNull JsForIn x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsFunction x, JsContext ctx) {
+    public void endVisit(@NotNull JsFunction x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsIf x, JsContext ctx) {
+    public void endVisit(@NotNull JsIf x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsInvocation x, JsContext ctx) {
+    public void endVisit(@NotNull JsInvocation x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsLabel x, JsContext ctx) {
+    public void endVisit(@NotNull JsLabel x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsName x, JsContext ctx) {
+    public void endVisit(@NotNull JsName x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsNameRef x, JsContext ctx) {
+    public void endVisit(@NotNull JsNameRef x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsNew x, JsContext ctx) {
+    public void endVisit(@NotNull JsNew x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsNullLiteral x, JsContext ctx) {
+    public void endVisit(@NotNull JsNullLiteral x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsNumberLiteral x, JsContext ctx) {
+    public void endVisit(@NotNull JsNumberLiteral x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsObjectLiteral x, JsContext ctx) {
+    public void endVisit(@NotNull JsObjectLiteral x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsParameter x, JsContext ctx) {
+    public void endVisit(@NotNull JsParameter x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsPostfixOperation x, JsContext ctx) {
+    public void endVisit(@NotNull JsPostfixOperation x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsPrefixOperation x, JsContext ctx) {
+    public void endVisit(@NotNull JsPrefixOperation x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsProgram x, JsContext ctx) {
+    public void endVisit(@NotNull JsProgram x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsProgramFragment x, JsContext ctx) {
+    public void endVisit(@NotNull JsProgramFragment x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsPropertyInitializer x, JsContext ctx) {
+    public void endVisit(@NotNull JsPropertyInitializer x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsRegExp x, JsContext ctx) {
+    public void endVisit(@NotNull JsRegExp x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsReturn x, JsContext ctx) {
+    public void endVisit(@NotNull JsReturn x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsStringLiteral x, JsContext ctx) {
+    public void endVisit(@NotNull JsStringLiteral x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsSwitch x, JsContext ctx) {
+    public void endVisit(@NotNull JsSwitch x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsLiteral.JsThisRef x, JsContext ctx) {
+    public void endVisit(@NotNull JsLiteral.JsThisRef x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsThrow x, JsContext ctx) {
+    public void endVisit(@NotNull JsThrow x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsTry x, JsContext ctx) {
+    public void endVisit(@NotNull JsTry x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsVars.JsVar x, JsContext ctx) {
+    public void endVisit(@NotNull JsVars.JsVar x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsVars x, JsContext ctx) {
+    public void endVisit(@NotNull JsVars x, @NotNull JsContext ctx) {
     }
 
-    public void endVisit(JsWhile x, JsContext ctx) {
+    public void endVisit(@NotNull JsWhile x, @NotNull JsContext ctx) {
     }
 
-    public boolean visit(JsArrayAccess x, JsContext ctx) {
+    public boolean visit(@NotNull JsArrayAccess x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsArrayLiteral x, JsContext ctx) {
+    public boolean visit(@NotNull JsArrayLiteral x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsBinaryOperation x, JsContext ctx) {
+    public boolean visit(@NotNull JsBinaryOperation x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsBlock x, JsContext ctx) {
+    public boolean visit(@NotNull JsBlock x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsLiteral.JsBooleanLiteral x, JsContext ctx) {
+    public boolean visit(@NotNull JsLiteral.JsBooleanLiteral x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsBreak x, JsContext ctx) {
+    public boolean visit(@NotNull JsBreak x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsCase x, JsContext ctx) {
+    public boolean visit(@NotNull JsCase x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsCatch x, JsContext ctx) {
+    public boolean visit(@NotNull JsCatch x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsConditional x, JsContext ctx) {
+    public boolean visit(@NotNull JsConditional x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsContinue x, JsContext ctx) {
+    public boolean visit(@NotNull JsContinue x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsDebugger x, JsContext ctx) {
+    public boolean visit(@NotNull JsDebugger x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsDefault x, JsContext ctx) {
+    public boolean visit(@NotNull JsDefault x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsDoWhile x, JsContext ctx) {
+    public boolean visit(@NotNull JsDoWhile x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsEmpty x, JsContext ctx) {
+    public boolean visit(@NotNull JsEmpty x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsExpressionStatement x, JsContext ctx) {
+    public boolean visit(@NotNull JsExpressionStatement x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsFor x, JsContext ctx) {
+    public boolean visit(@NotNull JsFor x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsForIn x, JsContext ctx) {
+    public boolean visit(@NotNull JsForIn x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsFunction x, JsContext ctx) {
+    public boolean visit(@NotNull JsFunction x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsIf x, JsContext ctx) {
+    public boolean visit(@NotNull JsIf x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsInvocation x, JsContext ctx) {
+    public boolean visit(@NotNull JsInvocation x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsLabel x, JsContext ctx) {
+    public boolean visit(@NotNull JsLabel x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsName x, JsContext ctx) {
+    public boolean visit(@NotNull JsName x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsNameRef x, JsContext ctx) {
+    public boolean visit(@NotNull JsNameRef x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsNew x, JsContext ctx) {
+    public boolean visit(@NotNull JsNew x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsNullLiteral x, JsContext ctx) {
+    public boolean visit(@NotNull JsNullLiteral x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsNumberLiteral x, JsContext ctx) {
+    public boolean visit(@NotNull JsNumberLiteral x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsObjectLiteral x, JsContext ctx) {
+    public boolean visit(@NotNull JsObjectLiteral x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsParameter x, JsContext ctx) {
+    public boolean visit(@NotNull JsParameter x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsPostfixOperation x, JsContext ctx) {
+    public boolean visit(@NotNull JsPostfixOperation x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsPrefixOperation x, JsContext ctx) {
+    public boolean visit(@NotNull JsPrefixOperation x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsProgram x, JsContext ctx) {
+    public boolean visit(@NotNull JsProgram x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsProgramFragment x, JsContext ctx) {
+    public boolean visit(@NotNull JsProgramFragment x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsPropertyInitializer x, JsContext ctx) {
+    public boolean visit(@NotNull JsPropertyInitializer x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsRegExp x, JsContext ctx) {
+    public boolean visit(@NotNull JsRegExp x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsReturn x, JsContext ctx) {
+    public boolean visit(@NotNull JsReturn x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsStringLiteral x, JsContext ctx) {
+    public boolean visit(@NotNull JsStringLiteral x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsSwitch x, JsContext ctx) {
+    public boolean visit(@NotNull JsSwitch x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsLiteral.JsThisRef x, JsContext ctx) {
+    public boolean visit(@NotNull JsLiteral.JsThisRef x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsThrow x, JsContext ctx) {
+    public boolean visit(@NotNull JsThrow x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsTry x, JsContext ctx) {
+    public boolean visit(@NotNull JsTry x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsVars.JsVar x, JsContext ctx) {
+    public boolean visit(@NotNull JsVars.JsVar x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsVars x, JsContext ctx) {
+    public boolean visit(@NotNull JsVars x, @NotNull JsContext ctx) {
         return true;
     }
 
-    public boolean visit(JsWhile x, JsContext ctx) {
+    public boolean visit(@NotNull JsWhile x, @NotNull JsContext ctx) {
         return true;
     }
 
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/FunctionReader.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/FunctionReader.kt
index e9864b48957..1d1e1cd688f 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/FunctionReader.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/FunctionReader.kt
@@ -149,9 +149,7 @@ private fun JsFunction.markInlineArguments(descriptor: CallableDescriptor) {
     }
 
     val visitor = object: JsVisitorWithContextImpl() {
-        override fun endVisit(x: JsInvocation?, ctx: JsContext<*>?) {
-            if (x == null || ctx == null) return
-
+        override fun endVisit(x: JsInvocation, ctx: JsContext<*>) {
             val qualifier: JsExpression?
             val namesSet: Set<JsName>
 
@@ -180,11 +178,11 @@ private fun replaceExternalNames(function: JsFunction, externalReplacements: Map
     if (replacements.isEmpty()) return
 
     val visitor = object: JsVisitorWithContextImpl() {
-        override fun endVisit(x: JsNameRef?, ctx: JsContext<*>?) {
-            if (x == null || x.getQualifier() != null) return
+        override fun endVisit(x: JsNameRef, ctx: JsContext<*>) {
+            if (x.getQualifier() != null) return
 
             replacements[x.getIdent()]?.let {
-                ctx?.replaceMe(it)
+                ctx.replaceMe(it)
             }
         }
     }
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/JsInliner.java b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/JsInliner.java
index a4b96b30dbc..a1c5695624f 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/JsInliner.java
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/JsInliner.java
@@ -68,7 +68,7 @@ public class JsInliner extends JsVisitorWithContextImpl {
     }
 
     @Override
-    public boolean visit(JsFunction function, JsContext context) {
+    public boolean visit(@NotNull JsFunction function, @NotNull JsContext context) {
         inliningContexts.push(new JsInliningContext(function));
         assert !inProcessFunctions.contains(function): "Inliner has revisited function";
         inProcessFunctions.add(function);
@@ -81,7 +81,7 @@ public class JsInliner extends JsVisitorWithContextImpl {
     }
 
     @Override
-    public void endVisit(JsFunction function, JsContext context) {
+    public void endVisit(@NotNull JsFunction function, @NotNull JsContext context) {
         super.endVisit(function, context);
         refreshLabelNames(getInliningContext().newNamingContext(), function);
 
@@ -99,7 +99,7 @@ public class JsInliner extends JsVisitorWithContextImpl {
     }
 
     @Override
-    public boolean visit(JsInvocation call, JsContext context) {
+    public boolean visit(@NotNull JsInvocation call, @NotNull JsContext context) {
         if (shouldInline(call) && canInline(call)) {
             JsFunction containingFunction = getCurrentNamedFunction();
             if (containingFunction != null) {
@@ -124,7 +124,7 @@ public class JsInliner extends JsVisitorWithContextImpl {
     }
 
     @Override
-    public void endVisit(JsInvocation x, JsContext ctx) {
+    public void endVisit(@NotNull JsInvocation x, @NotNull JsContext ctx) {
         JsCallInfo lastCallInfo = null;
 
         if (!inlineCallInfos.isEmpty()) {
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/NodeRemover.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/NodeRemover.kt
index 00423810be6..ee2cf2c58ce 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/NodeRemover.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/NodeRemover.kt
@@ -22,9 +22,7 @@ import com.google.dart.compiler.backend.js.ast.JsContext
 
 private class NodeRemover<T>(val klass: Class<T>, val predicate: (T) -> Boolean): JsVisitorWithContextImpl() {
 
-    override fun <T : JsNode?> doTraverse(node: T?, ctx: JsContext<*>?) {
-        if (node == null || ctx == null) return
-
+    override fun <T : JsNode> doTraverse(node: T, ctx: JsContext<*>) {
         if (klass.isInstance(node)) {
             val instance = klass.cast(node)!!
 
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedFunctionDefinitions.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedFunctionDefinitions.kt
index 3af1c75e1bf..90d15e39166 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedFunctionDefinitions.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedFunctionDefinitions.kt
@@ -66,8 +66,8 @@ private class UnusedLocalFunctionsCollector(functions: Map<JsName, JsFunction>)
         }
     }
 
-    override fun visit(x: JsPropertyInitializer?, ctx: JsContext<*>?): Boolean {
-        val value = x?.getValueExpr()
+    override fun visit(x: JsPropertyInitializer, ctx: JsContext<*>): Boolean {
+        val value = x.getValueExpr()
 
         return when (value) {
             is JsFunction -> !wasProcessed(value)
@@ -75,18 +75,16 @@ private class UnusedLocalFunctionsCollector(functions: Map<JsName, JsFunction>)
         }
     }
 
-    override fun visit(x: JsFunction?, ctx: JsContext<*>?): Boolean {
+    override fun visit(x: JsFunction, ctx: JsContext<*>): Boolean {
         return !(wasProcessed(x))
     }
 
-    override fun endVisit(x: JsFunction?, ctx: JsContext<*>?) {
-        if (x == null) return
-
+    override fun endVisit(x: JsFunction, ctx: JsContext<*>) {
         processed.add(x)
     }
 
-    override fun endVisit(x: JsNameRef?, ctx: JsContext<*>?) {
-        val name = x?.getName()
+    override fun endVisit(x: JsNameRef, ctx: JsContext<*>) {
+        val name = x.getName()
         if (isFunctionReference(x) && name != null) {
             tracker.markReachable(name)
         }
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedLocalFunctionDeclarations.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedLocalFunctionDeclarations.kt
index 1569f3c33a4..1fa6bf708b4 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedLocalFunctionDeclarations.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedLocalFunctionDeclarations.kt
@@ -45,9 +45,7 @@ private class UnusedInstanceCollector : JsVisitorWithContextImpl() {
     public val removableDeclarations: List<JsStatement>
         get() = tracker.removable
 
-    override fun visit(x: JsVars.JsVar?, ctx: JsContext<*>?): Boolean {
-        if (x == null) return false
-
+    override fun visit(x: JsVars.JsVar, ctx: JsContext<*>): Boolean {
         if (!isLocalFunctionDeclaration(x)) return super.visit(x, ctx)
 
         val name = x.getName()!!
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/ReferenceNameCollector.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/ReferenceNameCollector.kt
index cbef182a301..fb74d244ea2 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/ReferenceNameCollector.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/collectors/ReferenceNameCollector.kt
@@ -28,8 +28,8 @@ class ReferenceNameCollector : JsVisitorWithContextImpl() {
     public val references: List<JsName>
         get() = referenceSet.toList()
 
-    override fun endVisit(x: JsNameRef?, ctx: JsContext<*>?) {
-        val name = x?.getName()
+    override fun endVisit(x: JsNameRef, ctx: JsContext<*>) {
+        val name = x.getName()
         if (name != null) {
             referenceSet.add(name)
         }
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/LabelNameRefreshingVisitor.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/LabelNameRefreshingVisitor.kt
index ff22732ae44..bcb03d4e3ca 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/LabelNameRefreshingVisitor.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/LabelNameRefreshingVisitor.kt
@@ -24,10 +24,10 @@ import com.google.dart.compiler.backend.js.ast.JsContext
 import com.google.dart.compiler.backend.js.ast.JsLabel
 
 class LabelNameRefreshingVisitor(val context: NamingContext, val functionScope: JsFunctionScope) : JsVisitorWithContextImpl() {
-    override fun visit(x: JsFunction?, ctx: JsContext<*>?): Boolean = false
+    override fun visit(x: JsFunction, ctx: JsContext<*>): Boolean = false
 
-    override fun visit(x: JsLabel?, ctx: JsContext<*>?): Boolean {
-        val labelName = x!!.getName()
+    override fun visit(x: JsLabel, ctx: JsContext<*>): Boolean {
+        val labelName = x.getName()
         val freshName = functionScope.enterLabel(labelName.getIdent())
 
         if (freshName.getIdent() != labelName.getIdent()) {
@@ -37,7 +37,7 @@ class LabelNameRefreshingVisitor(val context: NamingContext, val functionScope:
         return super.visit(x, ctx)
     }
 
-    override fun endVisit(x: JsLabel?, ctx: JsContext<*>?) {
+    override fun endVisit(x: JsLabel, ctx: JsContext<*>) {
         super.endVisit(x, ctx)
         functionScope.exitLabel()
     }
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/NameReplacingVisitor.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/NameReplacingVisitor.kt
index 274f8c61bda..24c2043b42c 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/NameReplacingVisitor.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/NameReplacingVisitor.kt
@@ -27,18 +27,14 @@ import com.google.dart.compiler.backend.js.ast.JsLabel
 
 class NameReplacingVisitor(private val replaceMap: Map<JsName, JsExpression>) : JsVisitorWithContextImpl() {
 
-    override fun endVisit(x: JsNameRef?, ctx: JsContext<*>?) {
-        if (x == null || ctx == null) return
-
+    override fun endVisit(x: JsNameRef, ctx: JsContext<*>) {
         val replacement = replaceMap[x.getName()]
         if (replacement == null) return
 
         ctx.replaceMe(replacement)
     }
 
-    override fun endVisit(x: JsVars.JsVar?, ctx: JsContext<*>?) {
-        if (x == null || ctx == null) return
-
+    override fun endVisit(x: JsVars.JsVar, ctx: JsContext<*>) {
         val replacement = replaceMap[x.getName()]
         if (replacement is HasName) {
             val replacementVar = JsVars.JsVar(replacement.getName(), x.getInitExpression())
@@ -46,9 +42,7 @@ class NameReplacingVisitor(private val replaceMap: Map<JsName, JsExpression>) :
         }
     }
 
-    override fun endVisit(x: JsLabel?, ctx: JsContext<*>?) {
-        if (x == null || ctx == null) return
-
+    override fun endVisit(x: JsLabel, ctx: JsContext<*>) {
         val replacement = replaceMap[x.getName()]
         if (replacement is HasName) {
             val replacementLabel = JsLabel(replacement.getName(), x.getStatement())
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/ReturnReplacingVisitor.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/ReturnReplacingVisitor.kt
index ef5cee45eda..982849ade75 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/ReturnReplacingVisitor.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/ReturnReplacingVisitor.kt
@@ -33,16 +33,14 @@ class ReturnReplacingVisitor(private val resultRef: JsNameRef?, private val brea
     /**
      * Prevents replacing returns in object literal
      */
-    override fun visit(x: JsObjectLiteral?, ctx: JsContext<*>?): Boolean = false
+    override fun visit(x: JsObjectLiteral, ctx: JsContext<*>): Boolean = false
 
     /**
      * Prevents replacing returns in inner function
      */
-    override fun visit(x: JsFunction?, ctx: JsContext<*>?): Boolean = false
-
-    override fun endVisit(x: JsReturn?, ctx: JsContext<*>?) {
-        if (x == null || ctx == null) return
+    override fun visit(x: JsFunction, ctx: JsContext<*>): Boolean = false
 
+    override fun endVisit(x: JsReturn, ctx: JsContext<*>) {
         ctx.removeMe()
 
         val returnReplacement = getReturnReplacement(x.getExpression())
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/ThisReplacingVisitor.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/ThisReplacingVisitor.kt
index a3dfda47f89..13815ed438f 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/ThisReplacingVisitor.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/rewriters/ThisReplacingVisitor.kt
@@ -24,11 +24,11 @@ import com.google.dart.compiler.backend.js.ast.JsObjectLiteral
 import com.google.dart.compiler.backend.js.ast.JsVisitorWithContextImpl
 
 class ThisReplacingVisitor(private val thisReplacement: JsExpression) : JsVisitorWithContextImpl() {
-    override fun endVisit(x: JsLiteral.JsThisRef?, ctx: JsContext<*>?) {
-        ctx?.replaceMe(thisReplacement)
+    override fun endVisit(x: JsLiteral.JsThisRef, ctx: JsContext<*>) {
+        ctx.replaceMe(thisReplacement)
     }
 
-    override fun visit(x: JsFunction?, ctx: JsContext<*>?) = false
+    override fun visit(x: JsFunction, ctx: JsContext<*>) = false
 
-    override fun visit(x: JsObjectLiteral?, ctx: JsContext<*>?) = false
+    override fun visit(x: JsObjectLiteral, ctx: JsContext<*>) = false
 }