Confusion on usage of vmaf_model_colllection_load

[ThatNerdUKnow]

I was reading model.h and came across this function and I'm confused as to why it requires a pointer to a VmafModel as well as a VmafModelCollection. I did some more looking and from what I can tell the very first model in the model collection gets put into **model while the rest of the models go into **model_collection. What are we supposed to do with **model? and why doesn't the first model in the model collection json file get added to the model collection struct?

model.h

int vmaf_model_collection_load(VmafModel **model,
                               VmafModelCollection **model_collection,
                               VmafModelConfig *cfg,
                               const char *version);

read_json_model.c

function model_collection_parse
here's where I found where **model and **model_collection are being set

unsigned i = 0;
    while (json_peek(s) != JSON_OBJECT_END && !json_get_error(s)) {
        if (json_next(s) != JSON_STRING)
            return -EINVAL;

        const char *key = json_get_string(s, NULL);
        snprintf(generated_key, generated_key_sz, "%d", i);

        if (!strcmp(key, generated_key)) {
            VmafModel *m;
            err = vmaf_read_json_model(&m, &c, s);
            if (err) return err;

            if (i == 0) {
                 // First iteration of this loop. *model is set to m
                 // m is never added to the model collection on the first loop... why?
                *model = m; 
                c.name = cfg_name;
            } else {
                err = vmaf_model_collection_append(model_collection, m);
                if (err) return err;
            }

            sprintf((char*)c.name, "%s_%04d", name, ++i);
            continue;
        }

libvmaf.h

here's where we use our model collection. What are we supposed to be doing with the VmafModel pointer returned by vmaf_model_collection_load?

/**
 * Register feature extractors required by a specific `VmafModelCollection`
 * Like `vmaf_use_features_from_model()`, this function may be called
 * multiple times using different model collections.
 *
 * @param vmaf             The VMAF context allocated with `vmaf_init()`.
 *
 * @param model_collection Opaque model collection context.
 *
 *
 * @return 0 on success, or < 0 (a negative errno code) on error.
 */
int vmaf_use_features_from_model_collection(VmafContext *vmaf,
                                            VmafModelCollection *model_collection);

[nilfm]

cc: @kylophone, is there a reason for this?