Handling of empty filter
The current implementation is not able to handle an empty filter (i.e. an empty string ""). If FilterParser.parse("") is called, it returns the following response:
Invalid filter syntax. Please look at the additional info and examples about the filter parameter at https://docs.ohsome.org/ohsome-api. Detailed error message: line 1, column 1: whitespaces, not, (, KEY_STRING (a-z, 0-9, : or -), ", type or geometry expected, EOF encountered.
It would be nice if it could just ignore this filter then, similar to the behavior in the OSHDB.