How do I exclude files from a project in Kate?

I'm trying to exclude Ubuntu backup files from a project. Those are files ending with a tilde "~". I can get a Kate project to include list of all files in a folder, for example:

{
"name": "docs",
"files": [ {
"directory": "/home/Documents/"
} ]
}

And I can get it to include only backup files in a folder:

{
"name": "docs",
"files": [ {
"directory": "/home/Documents/",
"filters": [ ("*~")]
} ]
}

But my attempt to exclude those backup files actually includes them:

{
"name": "docs",
"files": [ {
"directory": "/home/Documents/",
"filters": [ !("*~")]
} ]
}

What can I do to exclude those files?