Cannot access empty property in query_type_numeric_range.inc on line 77

Hi,

i am developing a dependency filter that hides some facets depending of custom criteria, and i start my dev hiding all facets, when i do this i obtain this error:

Cannot access empty property in query_type_numeric_range.inc on line 77

It seems that when a facet is not being render because a dependency filter returns FALSE a check must be done in that line, at least this hides de error, not sure if there is a bigger problem with this.

I send a patch that checks if the variable single_key is initialized.

Best
David