The answer to whether or not to use filler will be dictated by the Welding Procedure Specification (WPS)that will be used on that joint. The WPS should be selected based on customer requirements and any national standards (ASME, API, AMS, AWS, MIL, etc...) you will be welding to and/or any NDE associated with the weld. Also, since no leg length is called out, a very small fillet with concave face would be possible with out the addition of filler metal. Lastly, if the welding process to be used is SMAW (stick) or GMAW (MIG) you must add filler by nature of the process.