Must be loading your data after BoxUtilModPlugin.initPre() has called
Typically, call BoxUtilModPlugin.initPre() in your mod's BaseModPlugin.onApplicationLoad()
And then, call the loading method after that
Your mod's data file can be place in anywhere

OBJ Data:
    Loading method: EntityShadingDataManager.loadModelDataCSV()
    For model, the .mtl file is not necessary; triangles and quads both ok; recommended to use a high-precision model.
    For Cinema 4D, should exchange the y-axis and z-axis.
    For performance, obj file shouldn't be bigger than 8 MiB.
    !!! DO NOT WITH ANY N-GONS !!!

Texture Data:
    Loading method: EntityShadingDataManager.loadTextureData()
    id: [ship id] for ship / [shot id] for missile / [weapon id] for weapon / [hull style id] for weapon cover / [battle objectives id] for battle objectives
    frame: optional; index of animated weapon, start from 0.
    type: ignore case; ENTITY / MISSILE / TURRET / HARDPOINT; and use "entity" type for all of ship / battle objectives
    subType: ignore case, only for weapon and weapon cover; BASE / BARREL / UNDER / COVERSMALL / COVERMEDIUM / COVERLARGE

Illuminant Data:
    Loading method: EntityShadingDataManager.loadIlluminantData()
    id: [shot id] for projectile / [weapon id] for beam / [engine style id] for ship engine(not for missile)
    type: ignore case; PROJECTILE / BEAM / ENGINE

Trail Data:
    Loading method: StaticTrailManager.loadTrailData()