ensure cast to class type is suggested when argument type is null (IDEA-159884)

java/java-analysis-impl/src/com/intellij/codeInsight/daemon/impl/quickfix/CastMethodArgumentFix.java

@@ -61,6 +61,9 @@ public class CastMethodArgumentFix extends MethodArgumentFix implements HighPrio
         if (parameterType == null) return false;
       }
       if (exprType instanceof PsiPrimitiveType && parameterType instanceof PsiClassType) {
+        if (PsiType.NULL.equals(exprType)) {
+          return true;
+        }
         parameterType = PsiPrimitiveType.getUnboxedType(parameterType);
         if (parameterType == null) return false;
       }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/castMethodParameters15/afterNullType.java

@@ -0,0 +1,9 @@
+// "Cast parameter to 'java.lang.String'" "true"
+class a {
+    void f(Long... l) {}
+    void f(String s) {}
+    void g() {
+        f((String) null);
+    }
+}
+

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/castMethodParameters15/beforeNullType.java

@@ -0,0 +1,9 @@
+// "Cast parameter to 'java.lang.String'" "true"
+class a {
+    void f(Long... l) {}
+    void f(String s) {}
+    void g() {
+        f(<caret>null);
+    }
+}
+