Please ensure to add com.google.gson.Gson;
If you are not sure, how to add external library, please refer to How to add external library
Since there is no conventional way of clearing console for Intelij, I had to apply a hack. Here is how to apply it.
You could assign a shortcut to Clear All on the Console from Preferences > Keymap. In the following screenshot I am assigning the shortcut ALT SHIFT 1 to clear the console.
To test this just place your cursor in the console and use that keystroke combination.
This particular solution is taken from Solution