KT-7695 Java to Kotlin converter incorrectly generates a cast to non-nullable type

#KT-7695 Fixed

j2k/src/org/jetbrains/kotlin/j2k/ExpressionConverter.kt

@@ -428,11 +428,14 @@ class DefaultExpressionConverter : JavaElementVisitor(), ExpressionConverter {
         val operandType = operand?.getType()
         val typeText = castType.getType().getCanonicalText()
         val typeConversion = PRIMITIVE_TYPE_CONVERSIONS[typeText]
+        val operandConverted = codeConverter.convertExpression(operand)
         if (operandType is PsiPrimitiveType && typeConversion != null) {
-            result = MethodCallExpression.buildNotNull(codeConverter.convertExpression(operand), typeConversion)
+            result = MethodCallExpression.buildNotNull(operandConverted, typeConversion)
         }
         else {
-            result = TypeCastExpression(typeConverter.convertType(castType.getType()), codeConverter.convertExpression(operand))
+            val typeConverted = typeConverter.convertType(castType.getType(),
+                                                          if (operandConverted.isNullable) Nullability.Nullable else Nullability.NotNull)
+            result = TypeCastExpression(typeConverted, operandConverted)
         }
     }
 

j2k/testData/fileOrElement/typeCastExpression/castNullable.java

@@ -0,0 +1,12 @@
+class A {
+    private String foo(Object o, boolean b) {
+        if (b) return (String) o;
+        return "";
+    }
+
+    void bar() {
+        if (foo(null, true) == null) {
+            System.out.println("null");
+        }
+    }
+}

j2k/testData/fileOrElement/typeCastExpression/castNullable.kt

@@ -0,0 +1,12 @@
+class A {
+    private fun foo(o: Any?, b: Boolean): String? {
+        if (b) return o as String?
+        return ""
+    }
+
+    fun bar() {
+        if (foo(null, true) == null) {
+            println("null")
+        }
+    }
+}

j2k/tests/org/jetbrains/kotlin/j2k/JavaToKotlinConverterForWebDemoTestGenerated.java

@@ -4180,6 +4180,12 @@ public class JavaToKotlinConverterForWebDemoTestGenerated extends AbstractJavaTo
             JetTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("j2k/testData/fileOrElement/typeCastExpression"), Pattern.compile("^(.+)\\.java$"), true);
         }
 
+        @TestMetadata("castNullable.java")
+        public void testCastNullable() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("j2k/testData/fileOrElement/typeCastExpression/castNullable.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("extendsWildcardCast.java")
         public void testExtendsWildcardCast() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("j2k/testData/fileOrElement/typeCastExpression/extendsWildcardCast.java");

j2k/tests/org/jetbrains/kotlin/j2k/JavaToKotlinConverterSingleFileTestGenerated.java

@@ -4180,6 +4180,12 @@ public class JavaToKotlinConverterSingleFileTestGenerated extends AbstractJavaTo
             JetTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("j2k/testData/fileOrElement/typeCastExpression"), Pattern.compile("^(.+)\\.java$"), true);
         }
 
+        @TestMetadata("castNullable.java")
+        public void testCastNullable() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("j2k/testData/fileOrElement/typeCastExpression/castNullable.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("extendsWildcardCast.java")
         public void testExtendsWildcardCast() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("j2k/testData/fileOrElement/typeCastExpression/extendsWildcardCast.java");