[Question] How could I fix this Editor error in Pokemon Essentials?

Hello there,
Whenever I go to the Editor in my game's folder and I edit something there (no matter what, the same problem always appear) when I'm done editing and I click "Save Changes" before exit , an error message pops up: (in this case, this error appeared when I tried to save changes after editing Regional Dexes):

Exception: NoMethodError
Message: undefined method `write' for nil:NilClass
Editor:134:in `pbSavePokemonData'
Editor2 #####:1698:in `pbRegionalNumbersEditor'
Editor2 #####:1625:in `loop'
Editor2 #####:1705:in `pbRegionalNumbersEditor'
EditorMain #####:122:in `pbEditorMenu'
EditorMain #####:122:in `pbFadeOutIn'
EditorMain #####:122:in `pbEditorMenu'
EditorMain #####:85:in `loop'
EditorMain #####:279:in `pbEditorMenu'
EditorMain #####:285

Does somebody know the cause of this error and the possible solution? An error like this appears no matter what I edit in the Editor, in this case was Regional Dexes section though, and it appears just after clicking "Save changes".

Maybe the cause was that I've been updating my computer's operation system, or maybe it has to do with the current version of Pokémon Essentials that I'm using, which is version 16.3
I'm using that version because I'm making a game only in Spanish, and versions of Essentials forward to v16.3 are all in English, as far as I know.

Thanks in advance for your help. I'd appreciate your insight on this.