@The Undying Nephalim I asked someone who actually know something about prog and then we found something. In the error, it specifies that the error is line 1452.
 
let popBonus = gameState.getTemplate(house).getPopulationBonus();
	Since the error type is "gameState.getTemplate(...) is null", and inside these brackets is house, we searched above how "house" was specified, we got to line 1450.
 
let house = gameState.applyCiv("structures/{civ}_house");
	So if you want to integrate this into the code :
 
this.buildings =
    {
        "ai_buildfield": {
            "default": [],
            "hylian": [ "structures/hylian_farmsteadA" ],
            "gerudo": [ "structures/gerudo_pigfarmA" ]
        },
        "ai_buildhouse": {
            "default": [],
            "hylian": [ "structures/hylian_housesA" ],
            "gerudo": [ "structures/gerudo_housesA" ]
        },
    };   
	You might make it here.
 
	It's just a possibility, after all !
 
	@niektb I can't find where the civ.json file is. Where is it, so I can try to find an answer here (even if I most likely won't since I haven't the Hyrule Conquest files).