Eliminate some warnings (mostly redundant is checks in whens)

idea/src/org/jetbrains/kotlin/idea/inspections/AddVarianceModifierInspection.kt

@@ -44,8 +44,7 @@ class AddVarianceModifierInspection : AbstractKotlinInspection() {
         for (member in klass.declarations + klass.primaryConstructorParameters) {
             val descriptor = when (member) {
                                  is KtParameter -> context.get(BindingContext.PRIMARY_CONSTRUCTOR_PARAMETER, member)
-                                 is KtDeclaration -> context.get(BindingContext.DECLARATION_TO_DESCRIPTOR, member)
-                                 else -> null
+                                 else -> context.get(BindingContext.DECLARATION_TO_DESCRIPTOR, member)
                              } as? MemberDescriptor ?: continue
             when (member) {
                 is KtClassOrObject -> {

idea/src/org/jetbrains/kotlin/idea/quickfix/createFromUsage/createVariable/CreateParameterByRefActionFactory.kt

@@ -136,12 +136,10 @@ fun KotlinType.hasTypeParametersToAdd(functionDescriptor: FunctionDescriptor, co
                     (functionDescriptor.containingDeclaration as? ClassDescriptorWithResolutionScopes)?.scopeForClassHeaderResolution
                 }
 
-                is FunctionDescriptor -> {
+                else -> {
                     val function = functionDescriptor.source.getPsi() as? KtFunction
                     function?.bodyExpression?.getResolutionScope(context, function.getResolutionFacade())
                 }
-
-                else -> null
             } ?: return true
 
     return typeParametersToAdd.any { scope.findClassifier(it.name, NoLookupLocation.FROM_IDE) != it }

idea/src/org/jetbrains/kotlin/idea/refactoring/kotlinRefactoringUtil.kt

@@ -968,7 +968,7 @@ fun KtNamedDeclaration.isCompanionMemberOf(klass: KtClassOrObject): Boolean {
 
 internal fun KtDeclaration.withHeaderImplementations(): List<KtDeclaration> {
     val header = liftToHeader() ?: return listOf(this)
-    val implementations = header.headerImplementations() ?: emptySet()
+    val implementations = header.headerImplementations()
     return listOf(header) + implementations
 }