diff --git a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/KotlinCallCompleter.kt b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/KotlinCallCompleter.kt
index 539d9d222a7..b4399c7ebc3 100644
--- a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/KotlinCallCompleter.kt
+++ b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/KotlinCallCompleter.kt
@@ -120,7 +120,7 @@ class KotlinCallCompleter(
             descriptorWithFreshTypes is PropertyDescriptor && descriptorWithFreshTypes.typeParameters.isNotEmpty() ->
                 // this code is very suspicious. Now it is very useful for BE, because they cannot do nothing with captured types,
                 // but it seems like temporary solution.
-                descriptorWithFreshTypes.substituteAndApproximateCapturedTypes(substitutor)!!
+                descriptorWithFreshTypes.substituteAndApproximateCapturedTypes(substitutor)
             else ->
                 descriptorWithFreshTypes
         }
diff --git a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/ResolutionParts.kt b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/ResolutionParts.kt
index e4feb509648..4b0485b348d 100644
--- a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/ResolutionParts.kt
+++ b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/ResolutionParts.kt
@@ -137,7 +137,7 @@ internal object CreateDescriptorWithFreshTypeVariables : ResolutionPart {
 
         // optimization
         if (typeArgumentMappingByOriginal == NoExplicitArguments) {
-            descriptorWithFreshTypes = candidateDescriptor.substitute(toFreshVariables)!!
+            descriptorWithFreshTypes = candidateDescriptor.substitute(toFreshVariables)
             csBuilder.simplify().let { assert(it.isEmpty) { "Substitutor should be empty: $it, call: $kotlinCall" } }
             return emptyList()
         }
@@ -166,7 +166,7 @@ internal object CreateDescriptorWithFreshTypeVariables : ResolutionPart {
          */
         val toFixedTypeParameters = csBuilder.simplify()
         // todo optimize -- composite substitutions before run safeSubstitute
-        descriptorWithFreshTypes = candidateDescriptor.substitute(toFreshVariables)!!.substitute(toFixedTypeParameters)!!
+        descriptorWithFreshTypes = candidateDescriptor.substitute(toFreshVariables).substitute(toFixedTypeParameters)
 
         return emptyList()
     }
diff --git a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/InferenceUtils.kt b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/InferenceUtils.kt
index 35d84b708f4..6d1415d61fa 100644
--- a/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/InferenceUtils.kt
+++ b/compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/InferenceUtils.kt
@@ -36,7 +36,7 @@ val CallableDescriptor.returnTypeOrNothing: UnwrappedType
 
 fun TypeSubstitutor.substitute(type: UnwrappedType): UnwrappedType = safeSubstitute(type, Variance.INVARIANT).unwrap()
 
-fun CallableDescriptor.substitute(substitutor: NewTypeSubstitutor): CallableDescriptor? {
+fun CallableDescriptor.substitute(substitutor: NewTypeSubstitutor): CallableDescriptor {
     val wrappedSubstitution = object : TypeSubstitution() {
         override fun get(key: KotlinType): TypeProjection? = null
         override fun prepareTopLevelType(topLevelType: KotlinType, position: Variance) = substitutor.safeSubstitute(topLevelType.unwrap())
@@ -44,7 +44,7 @@ fun CallableDescriptor.substitute(substitutor: NewTypeSubstitutor): CallableDesc
     return substitute(TypeSubstitutor.create(wrappedSubstitution))
 }
 
-fun CallableDescriptor.substituteAndApproximateCapturedTypes(substitutor: NewTypeSubstitutor): CallableDescriptor? {
+fun CallableDescriptor.substituteAndApproximateCapturedTypes(substitutor: NewTypeSubstitutor): CallableDescriptor {
     val wrappedSubstitution = object : TypeSubstitution() {
         override fun get(key: KotlinType): TypeProjection? = null
 
@@ -58,4 +58,4 @@ fun CallableDescriptor.substituteAndApproximateCapturedTypes(substitutor: NewTyp
     return substitute(TypeSubstitutor.create(wrappedSubstitution))
 }
 
-fun <E> MutableList<E>.trimToSize(newSize: Int) = subList(newSize, size).clear()
\ No newline at end of file
+internal fun <E> MutableList<E>.trimToSize(newSize: Int) = subList(newSize, size).clear()
\ No newline at end of file