From be22078bd1808805d32e81fc20645bb508185e94 Mon Sep 17 00:00:00 2001
From: Victor Petukhov <victor.petukhov@jetbrains.com>
Date: Mon, 24 May 2021 15:01:52 +0300
Subject: [PATCH] Return empty `NotFixedToInferredTypesSubstitutor` if the
 current substitutor is empty

---
 .../resolve/calls/inference/BuilderInferenceSession.kt     | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/inference/BuilderInferenceSession.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/inference/BuilderInferenceSession.kt
index 962ce7b3dcc..ba36babcfc1 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/inference/BuilderInferenceSession.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/inference/BuilderInferenceSession.kt
@@ -206,8 +206,11 @@ class BuilderInferenceSession(
 
     override fun currentConstraintSystem() = ConstraintStorage.Empty
 
-    fun getNotFixedToInferredTypesSubstitutor(): NewTypeSubstitutor =
-        ComposedSubstitutor(commonSystem.buildCurrentSubstitutor() as NewTypeSubstitutor, createNonFixedTypeToVariableSubstitutor())
+    fun getNotFixedToInferredTypesSubstitutor(): NewTypeSubstitutor {
+        val currentSubstitutor =
+            commonSystem.buildCurrentSubstitutor().cast<NewTypeSubstitutor>().takeIf { !it.isEmpty } ?: return EmptySubstitutor
+        return ComposedSubstitutor(currentSubstitutor, createNonFixedTypeToVariableSubstitutor())
+    }
 
     override fun inferPostponedVariables(
         lambda: ResolvedLambdaAtom,