Resource pack is failing if there are changes to font.

Resource pack works if there are no changes to font and even loads if there is old "pack_format", but fails to load if there are changes to font. (I'm talking about custom icons that replace text like "\uE001"...). I'm writing the code into "default.json" file that is in: ["resource pack name"/assets/minecraft/font/default.json] and takes png file in: ["resource pack name"/assets/minecraft/textures/font/"other files"]. Here is the code in the default.json file:

 
{
    "providers": [
        {
            "type": "bitmap",
            "file": "minecraft:font/icons/hotbars/thirst_filled.png",
            "ascent": 11,
            "height": 11,
            "chars": [
                "\uE001"
            ]
        }
    ]
}