One of Kotlin most prominent feature above Java is it’s null-safety feature. However, there’s a simple way that make it null, and the code still executable. Don’t believe? Try the below code. @Test fun forceNull() { val nullBody = """{ "nonNull" : null}""" val nullNonNull = Gson().fromJson(nullBody, MyData::class.java) System.out.println(nullNonNull) } data class MyData (val nonNullString :String) It’s also a possible pitfall in actual development environment, as some JSON result could be null, then we’ll get null in our non-null data class variable. So be careful when you deserialize your JSON. Hopes you watch out this pitfall, and may Kotlin or Gson have a way to deal with this better. Click “❤” below to share. Thanks! ~ Twitter:elye ; Facebook:elye