Make type parameter nullable as it should be

This change is needed, because in NI we perform a more strict check

compiler/backend/src/org/jetbrains/kotlin/codegen/inline/InliningContext.kt

@@ -85,7 +85,7 @@ open class InliningContext(
 
     fun subInlineWithClassRegeneration(
             generator: NameGenerator,
-            newTypeMappings: MutableMap<String, String>,
+            newTypeMappings: MutableMap<String, String?>,
             callSiteInfo: InlineCallSiteInfo
     ): InliningContext = RegeneratedClassContext(
             this, expressionMap, state, generator, TypeRemapper.createFrom(typeRemapper, newTypeMappings),

compiler/backend/src/org/jetbrains/kotlin/codegen/inline/MethodInliner.kt

@@ -53,7 +53,7 @@ class MethodInliner(
     //keeps order
     private val transformations = ArrayList<TransformationInfo>()
     //current state
-    private val currentTypeMapping = HashMap<String, String>()
+    private val currentTypeMapping = HashMap<String, String?>()
     private val result = InlineResult.create()
     private var lambdasFinallyBlocks: Int = 0
 

compiler/backend/src/org/jetbrains/kotlin/codegen/inline/TypeRemapper.kt

@@ -22,7 +22,7 @@ class TypeParameter(val oldName: String, val newName: String?, val isReified: Bo
 
 //typeMapping data could be changed outside through method processing
 class TypeRemapper private constructor(
-        private val typeMapping: MutableMap<String, String>,
+        private val typeMapping: MutableMap<String, String?>,
         val parent: TypeRemapper? = null,
         private val isRootInlineLambda: Boolean = false
 ) {
@@ -65,7 +65,7 @@ class TypeRemapper private constructor(
     companion object {
         @JvmStatic
         fun createRoot(formalTypeParameters: TypeParameterMappings?): TypeRemapper {
-            return TypeRemapper(HashMap<String, String>()).apply {
+            return TypeRemapper(HashMap<String, String?>()).apply {
                 formalTypeParameters?.forEach {
                     registerTypeParameter(it)
                 }
@@ -73,7 +73,7 @@ class TypeRemapper private constructor(
         }
 
         @JvmStatic
-        fun createFrom(mappings: MutableMap<String, String>): TypeRemapper {
+        fun createFrom(mappings: MutableMap<String, String?>): TypeRemapper {
             return TypeRemapper(mappings)
         }
 
@@ -83,7 +83,7 @@ class TypeRemapper private constructor(
             return TypeRemapper(createNewAndMerge(parentRemapper, mappings), parentRemapper, isRootInlineLambda)
         }
 
-        private fun createNewAndMerge(remapper: TypeRemapper, additionalTypeMappings: Map<String, String?>): MutableMap<String, String> {
+        private fun createNewAndMerge(remapper: TypeRemapper, additionalTypeMappings: Map<String, String?>): MutableMap<String, String?> {
             return HashMap(remapper.typeMapping).apply {
                 this += additionalTypeMappings
             }