If you create a new pxdb_collection object and
immediately try to call execute(), the expected
behavior would be to get all objects of that datatype.
However, it generates an error. This means all
pxdb_collection objects must be passed a filter or
search object, even when they are filtering nothing.
Either by default a filter object needs to be created
and passed (the current workaround) or the collection
class needs to be updated to generate basic sql when no
filter is passed.