Thanks for creating this mod! Would it be possible for you to add documentation that paths containing a /, \, or : (in other words, if your image file is NOT in the root directory of your server folder) need to be escaped with single or double quotation marks? I was not familiar with this part of Brigadier, and I would imagine less technical users will be even more confused. Thanks!

TL;DR

/mapcreate example.jpg VALID
/mapcreate "example.jpg" VALID
/mapcreate 'example.jpg' VALID
/mapcreate "https://example.com/example.jpg" VALID
/mapcreate "examplefolder/example.jpg" VALID

/mapcreate https://example.com/example.jpg INVALID
/mapcreate examplefolder/example.jpg INVALID

I could probably get around to documenting that, a more ideal solution would be to try and make it so that the quotes aren't needed however

Quotes are no longer needed as of e1f171a.