diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/FunctionCodegen.java b/compiler/backend/src/org/jetbrains/kotlin/codegen/FunctionCodegen.java
index 6eaefbbcaa7..24b1673fe49 100644
--- a/compiler/backend/src/org/jetbrains/kotlin/codegen/FunctionCodegen.java
+++ b/compiler/backend/src/org/jetbrains/kotlin/codegen/FunctionCodegen.java
@@ -825,12 +825,12 @@ public class FunctionCodegen {
         endVisit(mv, "bridge method", origin);
     }
 
-    public void genDelegate(FunctionDescriptor functionDescriptor, FunctionDescriptor overriddenDescriptor, StackValue field) {
+    public void genDelegate(@NotNull FunctionDescriptor functionDescriptor, FunctionDescriptor overriddenDescriptor, StackValue field) {
         genDelegate(functionDescriptor, overriddenDescriptor.getOriginal(), (ClassDescriptor) overriddenDescriptor.getContainingDeclaration(), field);
     }
 
     public void genDelegate(
-            final FunctionDescriptor delegateFunction,
+            @NotNull final FunctionDescriptor delegateFunction,
             final FunctionDescriptor delegatedTo,
             final ClassDescriptor toClass,
             final StackValue field
diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/ImplementationBodyCodegen.java b/compiler/backend/src/org/jetbrains/kotlin/codegen/ImplementationBodyCodegen.java
index 63390395732..b7235b9b8ed 100644
--- a/compiler/backend/src/org/jetbrains/kotlin/codegen/ImplementationBodyCodegen.java
+++ b/compiler/backend/src/org/jetbrains/kotlin/codegen/ImplementationBodyCodegen.java
@@ -496,6 +496,10 @@ public class ImplementationBodyCodegen extends ClassBodyCodegen {
                     KotlinBuiltIns.getInstance().getBoolean(),
                     KotlinBuiltIns.getInstance().getAny()
             );
+
+            assert equalsFunction != null : String.format("Should be called only for classes with non-trivial '%s'. In %s, %s",
+                                                          CodegenUtil.EQUALS_METHOD_NAME, descriptor.getName(), descriptor);
+
             MethodContext context = ImplementationBodyCodegen.this.context.intoFunction(equalsFunction);
             MethodVisitor mv = v.newMethod(OtherOrigin(equalsFunction), ACC_PUBLIC, "equals", "(Ljava/lang/Object;)Z", null, null);
             InstructionAdapter iv = new InstructionAdapter(mv);
@@ -565,6 +569,10 @@ public class ImplementationBodyCodegen extends ClassBodyCodegen {
                     descriptor, Name.identifier(CodegenUtil.HASH_CODE_METHOD_NAME),
                     KotlinBuiltIns.getInstance().getInt()
             );
+
+            assert hashCodeFunction != null : String.format("Should be called only for classes with non-trivial '%s'. In %s, %s",
+                                                            CodegenUtil.HASH_CODE_METHOD_NAME, descriptor.getName(), descriptor);
+
             MethodContext context = ImplementationBodyCodegen.this.context.intoFunction(hashCodeFunction);
             MethodVisitor mv = v.newMethod(OtherOrigin(hashCodeFunction), ACC_PUBLIC, "hashCode", "()I", null, null);
             InstructionAdapter iv = new InstructionAdapter(mv);
@@ -617,6 +625,10 @@ public class ImplementationBodyCodegen extends ClassBodyCodegen {
                     descriptor, Name.identifier(CodegenUtil.TO_STRING_METHOD_NAME),
                     KotlinBuiltIns.getInstance().getString()
             );
+
+            assert toString != null : String.format("Should be called only for classes with non-trivial '%s'. In %s, %s",
+                                                    CodegenUtil.TO_STRING_METHOD_NAME, descriptor.getName(), descriptor);
+
             MethodContext context = ImplementationBodyCodegen.this.context.intoFunction(toString);
             MethodVisitor mv = v.newMethod(OtherOrigin(toString), ACC_PUBLIC, "toString", "()Ljava/lang/String;", null, null);
             InstructionAdapter iv = new InstructionAdapter(mv);
@@ -1603,7 +1615,7 @@ public class ImplementationBodyCodegen extends ClassBodyCodegen {
         }
     }
 
-    public void addClassObjectPropertyToCopy(PropertyDescriptor descriptor, Object defaultValue) {
+    public void addClassObjectPropertyToCopy(@NotNull PropertyDescriptor descriptor, Object defaultValue) {
         if (classObjectPropertiesToCopy == null) {
             classObjectPropertiesToCopy = new ArrayList<PropertyAndDefaultValue>();
         }
@@ -1623,7 +1635,7 @@ public class ImplementationBodyCodegen extends ClassBodyCodegen {
         public final PropertyDescriptor descriptor;
         public final Object defaultValue;
 
-        public PropertyAndDefaultValue(PropertyDescriptor descriptor, Object defaultValue) {
+        public PropertyAndDefaultValue(@NotNull PropertyDescriptor descriptor, Object defaultValue) {
             this.descriptor = descriptor;
             this.defaultValue = defaultValue;
         }
diff --git a/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/JvmDeclarationOrigin.kt b/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/JvmDeclarationOrigin.kt
index af874c7cded..a7cbf765833 100644
--- a/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/JvmDeclarationOrigin.kt
+++ b/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/JvmDeclarationOrigin.kt
@@ -54,9 +54,9 @@ public fun OtherOrigin(element: PsiElement?, descriptor: DeclarationDescriptor?)
             JvmDeclarationOrigin.NO_ORIGIN
         else JvmDeclarationOrigin(OTHER, element, descriptor)
 
-public fun OtherOrigin(element: PsiElement?): JvmDeclarationOrigin = OtherOrigin(element, null)
+public fun OtherOrigin(element: PsiElement): JvmDeclarationOrigin = OtherOrigin(element, null)
 
-public fun OtherOrigin(descriptor: DeclarationDescriptor?): JvmDeclarationOrigin = OtherOrigin(null, descriptor)
+public fun OtherOrigin(descriptor: DeclarationDescriptor): JvmDeclarationOrigin = OtherOrigin(null, descriptor)
 
 public fun PackageFacade(descriptor: PackageFragmentDescriptor): JvmDeclarationOrigin = JvmDeclarationOrigin(PACKAGE_FACADE, null, descriptor)
 public fun PackagePart(file: JetFile, descriptor: PackageFragmentDescriptor): JvmDeclarationOrigin = JvmDeclarationOrigin(PACKAGE_PART, file, descriptor)