Missing facetapi_map_date callback on non-search pages with date_range facet in block

Using the date_range query type and widget on the "created" date facet displayed in a block results in the following warning:

Warning: call_user_func() expects parameter 1 to be a valid callback, function 'facetapi_map_date' not found or invalid function name in FacetapiFacetProcessor->mapValues() (line 1502 of .../htdocs/sites/all/modules/facetapi/plugins/facetapi/adapter.inc).

This is reported on non-search pages on my site (this instance came from <front>) which uses apachesolr and facetapi. The date query type and links widget did not display the problem.

Adding a call:

module_load_include('inc', 'facetapi', 'facetapi.callbacks');

in the Drupal_Apachesolr_Facetapi_QueryType_DateRangeQueryType::build() method seems to have resolved the problem for me. I have no idea if this is the correct place for this change or whether it'll be necessary for the Search backend too, hence the lack of a patch.