private <T, Y> void cacheNullLoader(Class<T> modelClass, Class<Y> resourceClass) {
        cacheModelLoader(modelClass, resourceClass, NULL_MODEL_LOADER);
    }
Returns a {@link ModelLoader} for the given model and resource classes by either returning a cached
{@link ModelLoader} or building a new a new {@link ModelLoader} using registered {@link ModelLoaderFactory}s.
Returns null if no {@link ModelLoaderFactory} is registered for the given classes.

@param modelClass The model class.
@param resourceClass The resource class.
@param <T> The type of the model.
@param <Y> The type of the resource.
core/src/main/java/com/bumptech/glide/load/model/GenericLoaderFactory.java