com.google.firebase.database.DatabaseException: Serializing Arrays is not supported, please use Lists instead

I've managed to find the reason causing this crash. I installed the app on another device running Android 5.x and Firebase threw a much less confusing exception there:

com.google.firebase.database.DatabaseException: No properties to serialize found on class android.graphics.Paint$Align

It appeared that Firebase (unlike Gson) tries to serialize all possible getters even though they don't have direct connection with global variables (class members / fields), in my particular case one of my objects contained a method returning Drawable - getDrawable(). Obviously, Firebase doesn't know how to convert drawable into json.

Interesting moment (probably a bug in Firebase SDK): on my older device running Android 4.4.1 I still get my original exception in the same project and configuration:

Caused by: com.google.firebase.database.DatabaseException: Serializing Arrays is not supported, please use Lists instead

In case this helps others that are receiving the same error, I was getting the same error and the solution ended up being the following for me:

Changing:

databaseReference.child("somechild").setValue(etName.getText());

To:

databaseReference.child("somechild").setValue(etName.getText().toString());

As @fraggjkee points out, Firebase attempts to serialize getters, and this was the similar issue here with firebase attempting to serialize the result of the .getText().

Hope this helps others!

Add @Exclude to the functions that FB tries to interpret, like those that return a Drawable.

@Exclude
public Drawable getUnitColorImage(){
    return TextDrawable.builder().buildRound("", prefColor);
}