code cleanup: core modules

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/FlexibleTypeCapabilitiesDeserializer.kt

@@ -19,7 +19,7 @@ package org.jetbrains.kotlin.serialization.deserialization
 import org.jetbrains.kotlin.types.DynamicTypeCapabilities
 import org.jetbrains.kotlin.types.FlexibleTypeCapabilities
 
-trait FlexibleTypeCapabilitiesDeserializer {
+interface FlexibleTypeCapabilitiesDeserializer {
     object ThrowException : FlexibleTypeCapabilitiesDeserializer {
         override fun capabilitiesById(id: String): FlexibleTypeCapabilities? {
             throw IllegalArgumentException("Capabilities not found by ThrowException manager: $id")

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/LocalClassResolver.kt

@@ -19,6 +19,6 @@ package org.jetbrains.kotlin.serialization.deserialization
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.name.ClassId
 
-public trait LocalClassResolver {
+public interface LocalClassResolver {
     public fun resolveLocalClass(classId: ClassId): ClassDescriptor?
 }

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/descriptors/DeserializedCallableMemberDescriptor.kt

@@ -20,7 +20,7 @@ import org.jetbrains.kotlin.serialization.ProtoBuf
 import org.jetbrains.kotlin.serialization.deserialization.NameResolver
 import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor
 
-public trait DeserializedCallableMemberDescriptor: CallableMemberDescriptor {
+public interface DeserializedCallableMemberDescriptor: CallableMemberDescriptor {
     public val proto: ProtoBuf.Callable
     public val nameResolver: NameResolver
 }

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/descriptors/DeserializedMemberScope.kt

@@ -69,7 +69,7 @@ public abstract class DeserializedMemberScope protected constructor(
                 protos = ArrayList(1)
                 map.put(key, protos)
             }
-            protos!!.add(memberProto)
+            protos.add(memberProto)
         }
         return map
     }

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/findClassInModule.kt

@@ -23,7 +23,7 @@ import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.name.ClassId
 
 public fun ModuleDescriptor.findClassAcrossModuleDependencies(classId: ClassId): ClassDescriptor? {
-    val packageViewDescriptor = getPackage(classId.getPackageFqName()) ?: return null
+    val packageViewDescriptor = getPackage(classId.getPackageFqName())
     val segments = classId.getRelativeClassName().pathSegments()
     val topLevelClass = packageViewDescriptor.memberScope.getClassifier(segments.first()) as? ClassDescriptor ?: return null
     var result = topLevelClass