do null checks after assignment so that default==null is covered

test/transform/resource/before/SuperBuilderWithNonNull.java

@@ -0,0 +1,20 @@
+import java.util.List;
+
+public class SuperBuilderWithNonNull {
+	@lombok.experimental.SuperBuilder
+	public static class Parent {
+		@lombok.NonNull
+		@lombok.Builder.Default
+		String nonNullParentField = "default";
+	}
+	
+	@lombok.experimental.SuperBuilder
+	public static class Child extends Parent {
+		@lombok.NonNull
+		String nonNullChildField;
+	}
+	
+	public static void test() {
+		Child x = Child.builder().nonNullChildField("child").nonNullParentField("parent").build();
+	}
+}