diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/ClassNameCollectionClassBuilderFactory.kt b/compiler/backend/src/org/jetbrains/kotlin/codegen/ClassNameCollectionClassBuilderFactory.kt
index 515e59dee66..5b6374bc9f4 100644
--- a/compiler/backend/src/org/jetbrains/kotlin/codegen/ClassNameCollectionClassBuilderFactory.kt
+++ b/compiler/backend/src/org/jetbrains/kotlin/codegen/ClassNameCollectionClassBuilderFactory.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2015 JetBrains s.r.o.
+ * Copyright 2010-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -42,7 +42,7 @@ abstract class ClassNameCollectionClassBuilderFactory(
 
         override fun getDelegate() = _delegate
 
-        private var classInternalName: String? = null
+        private lateinit var classInternalName: String
 
         override fun defineClass(origin: PsiElement?, version: Int, access: Int, name: String, signature: String?, superName: String, interfaces: Array<out String>) {
             classInternalName = name
@@ -50,9 +50,7 @@ abstract class ClassNameCollectionClassBuilderFactory(
         }
 
         override fun done() {
-            if (classInternalName != null) {
-                handleClashingNames(classInternalName!!, classCreatedFor)
-            }
+            handleClashingNames(classInternalName, classCreatedFor)
             super.done()
         }
     }
diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/SignatureCollectingClassBuilderFactory.kt b/compiler/backend/src/org/jetbrains/kotlin/codegen/SignatureCollectingClassBuilderFactory.kt
index a6fdc715afd..ed1e231a41c 100644
--- a/compiler/backend/src/org/jetbrains/kotlin/codegen/SignatureCollectingClassBuilderFactory.kt
+++ b/compiler/backend/src/org/jetbrains/kotlin/codegen/SignatureCollectingClassBuilderFactory.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2015 JetBrains s.r.o.
+ * Copyright 2010-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -32,7 +32,7 @@ abstract class SignatureCollectingClassBuilderFactory(
 
     protected abstract fun handleClashingSignatures(data: ConflictingJvmDeclarationsData)
     protected abstract fun onClassDone(classOrigin: JvmDeclarationOrigin,
-                                       classInternalName: String?,
+                                       classInternalName: String,
                                        signatures: MultiMap<RawSignature, JvmDeclarationOrigin>)
 
     override fun newClassBuilder(origin: JvmDeclarationOrigin): DelegatingClassBuilder {
@@ -46,7 +46,7 @@ abstract class SignatureCollectingClassBuilderFactory(
 
         override fun getDelegate() = _delegate
 
-        private var classInternalName: String? = null
+        private lateinit var classInternalName: String
 
         private val signatures = LinkedMultiMap<RawSignature, JvmDeclarationOrigin>()
 
diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/state/BuilderFactoryForDuplicateSignatureDiagnostics.kt b/compiler/backend/src/org/jetbrains/kotlin/codegen/state/BuilderFactoryForDuplicateSignatureDiagnostics.kt
index aae4560b655..63702b6ff03 100644
--- a/compiler/backend/src/org/jetbrains/kotlin/codegen/state/BuilderFactoryForDuplicateSignatureDiagnostics.kt
+++ b/compiler/backend/src/org/jetbrains/kotlin/codegen/state/BuilderFactoryForDuplicateSignatureDiagnostics.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2015 JetBrains s.r.o.
+ * Copyright 2010-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -91,7 +91,7 @@ class BuilderFactoryForDuplicateSignatureDiagnostics(
 
     override fun onClassDone(
             classOrigin: JvmDeclarationOrigin,
-            classInternalName: String?,
+            classInternalName: String,
             signatures: MultiMap<RawSignature, JvmDeclarationOrigin>
     ) {
         reportDiagnosticsTasks.add { reportClashingSignaturesInHierarchy(classOrigin, classInternalName, signatures) }
@@ -99,7 +99,7 @@ class BuilderFactoryForDuplicateSignatureDiagnostics(
 
     private fun reportClashingSignaturesInHierarchy(
             classOrigin: JvmDeclarationOrigin,
-            classInternalName: String?,
+            classInternalName: String,
             signatures: MultiMap<RawSignature, JvmDeclarationOrigin>
     ) {
         val descriptor = classOrigin.descriptor
diff --git a/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/ConflictingJvmDeclarationsData.kt b/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/ConflictingJvmDeclarationsData.kt
index 5f1857575fe..d6835dceefb 100644
--- a/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/ConflictingJvmDeclarationsData.kt
+++ b/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/ConflictingJvmDeclarationsData.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2015 JetBrains s.r.o.
+ * Copyright 2010-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,7 +17,7 @@
 package org.jetbrains.kotlin.resolve.jvm.diagnostics
 
 class ConflictingJvmDeclarationsData(
-        val classInternalName: String?,
+        val classInternalName: String,
         val classOrigin: JvmDeclarationOrigin,
         val signature: RawSignature,
         val signatureOrigins: Collection<JvmDeclarationOrigin>
diff --git a/plugins/annotation-collector/src/org/jetbrains/kotlin/annotation/AnnotationCollectorExtension.kt b/plugins/annotation-collector/src/org/jetbrains/kotlin/annotation/AnnotationCollectorExtension.kt
index 2e710fa372d..c35d6bda52b 100644
--- a/plugins/annotation-collector/src/org/jetbrains/kotlin/annotation/AnnotationCollectorExtension.kt
+++ b/plugins/annotation-collector/src/org/jetbrains/kotlin/annotation/AnnotationCollectorExtension.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2015 JetBrains s.r.o.
+ * Copyright 2010-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -101,9 +101,9 @@ abstract class AnnotationCollectorExtensionBase(val supportInheritedAnnotations:
             }
         }
 
-        private var currentClassSimpleName: String? = null
+        private lateinit var currentClassSimpleName: String
 
-        private var currentPackageName: String? = null
+        private lateinit var currentPackageName: String
 
         override fun getVisitor() = classVisitor
 
@@ -184,13 +184,13 @@ abstract class AnnotationCollectorExtensionBase(val supportInheritedAnnotations:
 
             try {
                 val annotationId = shortenedAnnotationCache.save(annotationFqName, writer)
-                val packageName = this.currentPackageName!!
+                val packageName = this.currentPackageName
 
                 val packageNameId = if (!packageName.isEmpty())
                     shortenedPackageNameCache.save(packageName, writer)
                 else null
 
-                val className = this.currentClassSimpleName!!
+                val className = this.currentClassSimpleName
                 val outputClassName = getOutputClassName(packageNameId, className)
                 val elementName = if (name != null) " $name" else ""