diff --git a/core/descriptors/src/org/jetbrains/kotlin/resolve/calls/inference/ConstraintSystemImpl.kt b/core/descriptors/src/org/jetbrains/kotlin/resolve/calls/inference/ConstraintSystemImpl.kt
index da08f89bdd2..47817f8ae1a 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/resolve/calls/inference/ConstraintSystemImpl.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/resolve/calls/inference/ConstraintSystemImpl.kt
@@ -525,7 +525,7 @@ private fun TypeSubstitutor.setApproximateCapturedTypes(): TypeSubstitutor {
 }
 
 private class SubstitutionWithCapturedTypeApproximation(val substitution: TypeSubstitution) : TypeSubstitution() {
-    override fun get(key: TypeConstructor?) = substitution[key]
+    override fun get(key: TypeConstructor) = substitution[key]
     override fun isEmpty() = substitution.isEmpty()
     override fun approximateCapturedTypes() = true
 }
diff --git a/core/descriptors/src/org/jetbrains/kotlin/types/CapturedTypeApproximation.kt b/core/descriptors/src/org/jetbrains/kotlin/types/CapturedTypeApproximation.kt
index 18bd22195c7..3b8da38336f 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/types/CapturedTypeApproximation.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/types/CapturedTypeApproximation.kt
@@ -90,8 +90,8 @@ public fun approximateCapturedTypesIfNecessary(typeProjection: TypeProjection?):
 
 private fun substituteCapturedTypes(typeProjection: TypeProjection): TypeProjection? {
     val typeSubstitutor = TypeSubstitutor.create(object : TypeSubstitution() {
-        override fun get(typeConstructor: TypeConstructor?): TypeProjection? {
-            return (typeConstructor as? CapturedTypeConstructor)?.typeProjection
+        override fun get(key: TypeConstructor): TypeProjection? {
+            return (key as? CapturedTypeConstructor)?.typeProjection
         }
     })
     return typeSubstitutor.substituteWithoutApproximation(typeProjection)
diff --git a/core/descriptors/src/org/jetbrains/kotlin/types/TypeSubstitution.kt b/core/descriptors/src/org/jetbrains/kotlin/types/TypeSubstitution.kt
index cabf947aa4d..345a803cbb9 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/types/TypeSubstitution.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/types/TypeSubstitution.kt
@@ -14,36 +14,22 @@
  * limitations under the License.
  */
 
-package org.jetbrains.kotlin.types;
+package org.jetbrains.kotlin.types
 
-import org.jetbrains.annotations.Nullable;
+import kotlin.platform.platformStatic
 
 public abstract class TypeSubstitution {
-    public static final TypeSubstitution EMPTY = new TypeSubstitution() {
-        @Override
-        public TypeProjection get(TypeConstructor key) {
-            return null;
+    companion object {
+        platformStatic public val EMPTY: TypeSubstitution = object : TypeSubstitution() {
+            override fun get(key: TypeConstructor) = null
+            override fun isEmpty() = true
+            override fun toString() = "Empty TypeSubstitution"
         }
-
-        @Override
-        public boolean isEmpty() {
-            return true;
-        }
-
-        @Override
-        public String toString() {
-            return "Empty TypeSubstitution";
-        }
-    };
-
-    @Nullable
-    public abstract TypeProjection get(TypeConstructor key);
-
-    public boolean isEmpty() {
-        return false;
     }
 
-    public boolean approximateCapturedTypes() {
-        return false;
-    }
+    public abstract fun get(key: TypeConstructor): TypeProjection?
+
+    public open fun isEmpty(): Boolean = false
+
+    public open fun approximateCapturedTypes(): Boolean = false
 }