Fix handling of nullable types in LetImplementInterfaceFix #KT-11404

idea/src/org/jetbrains/kotlin/idea/quickfix/LetImplementInterfaceFix.kt

@@ -38,15 +38,19 @@ class LetImplementInterfaceFix(
 
     private fun KotlinType.renderShort() = IdeDescriptorRenderers.SOURCE_CODE_SHORT_NAMES_IN_TYPES.renderType(this)
 
-    private val expectedTypeName = expectedType.renderShort()
+    private val expectedTypeName: String
 
-    private val expectedTypeNameSourceCode = IdeDescriptorRenderers.SOURCE_CODE.renderType(expectedType)
+    private val expectedTypeNameSourceCode: String
 
     private val prefix: String
 
     private val validExpectedType: Boolean
 
     init {
+        val expectedTypeNotNullable = TypeUtils.makeNotNullable(expectedType)
+        expectedTypeName = expectedTypeNotNullable.renderShort()
+        expectedTypeNameSourceCode = IdeDescriptorRenderers.SOURCE_CODE.renderType(expectedTypeNotNullable)
+
         val verb = if (expressionType.isInterface()) "extend" else "implement"
         prefix = "Let '${expressionType.renderShort()}' $verb"
 

idea/testData/quickfix/typeMismatch/letClassImplementInterfaceNullable.kt

@@ -0,0 +1,13 @@
+// "Let 'B' implement interface 'A'" "true"
+package let.implement
+
+fun bar() {
+    foo(B()<caret>)
+}
+
+
+fun foo(a: A?) {
+}
+
+interface A
+class B

idea/testData/quickfix/typeMismatch/letClassImplementInterfaceNullable.kt.after

@@ -0,0 +1,13 @@
+// "Let 'B' implement interface 'A'" "true"
+package let.implement
+
+fun bar() {
+    foo(B()<caret>)
+}
+
+
+fun foo(a: A?) {
+}
+
+interface A
+class B : A

idea/tests/org/jetbrains/kotlin/idea/quickfix/QuickFixTestGenerated.java

@@ -7366,6 +7366,13 @@ public class QuickFixTestGenerated extends AbstractQuickFixTest {
             doTest(fileName);
         }
 
+        @TestMetadata("letClassImplementInterfaceNullable.kt")
+        public void testLetClassImplementInterfaceNullable() throws Exception {
+            String fileName =
+                    KotlinTestUtils.navigationMetadata("idea/testData/quickfix/typeMismatch/letClassImplementInterfaceNullable.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("letInterfaceExtendInterface.kt")
         public void testLetInterfaceExtendInterface() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/quickfix/typeMismatch/letInterfaceExtendInterface.kt");