`fallbackToBaseModel` is true in `ModelStore#get` when `returnModelInstance` is true. In all other cases, it defaults to false.

This option makes `getModel` return an instance of `baseModel` when the path does not exist. We need this behavior for instances where a collection uses `BaseModel`. In that case, `ModelStore#get` passes a `collectionName` as the path instead of a `modelName`.

We could make this behavior the default (and remove the `fallbackToBaseModel` parameter) without causing any tests to fail, but I elected to make this behavior optional because I can imagine scenarios in which you would want an exception when passing a non-existent path to `getModel`.

Another approach would be to leave `getModel` unchanged and handle the exception in `ModelStore#get`, but that seems like it would lead to needless code repetition.