Do not generate CHECKCAST after 'null' literal

#KT-15411 Fixed

compiler/backend/src/org/jetbrains/kotlin/codegen/StackValue.java

@@ -810,7 +810,9 @@ public abstract class StackValue {
                 v.aconst(value);
             }
 
-            coerceTo(type, v);
+            if (value != null || AsmUtil.isPrimitive(type)) {
+                coerceTo(type, v);
+            }
         }
     }
 

compiler/testData/codegen/bytecodeText/checkcast/kt15411.kt

@@ -0,0 +1,15 @@
+// KT-15411 Unnecessary CHECKCAST bytecode when dealing with null
+
+fun test1(): String? {
+    return null
+}
+
+fun test2(): BooleanArray? {
+    return null
+}
+
+fun test3(): Unit? {
+    return null
+}
+
+// 0 CHECKCAST

compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java

@@ -612,6 +612,21 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
         }
     }
 
+    @TestMetadata("compiler/testData/codegen/bytecodeText/checkcast")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class Checkcast extends AbstractBytecodeTextTest {
+        public void testAllFilesPresentInCheckcast() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/bytecodeText/checkcast"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.ANY, true);
+        }
+
+        @TestMetadata("kt15411.kt")
+        public void testKt15411() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/checkcast/kt15411.kt");
+            doTest(fileName);
+        }
+    }
+
     @TestMetadata("compiler/testData/codegen/bytecodeText/coercionToUnitOptimization")
     @TestDataPath("$PROJECT_ROOT")
     @RunWith(JUnit3RunnerWithInners.class)