Dereference null return value

If the function actually returns a null value, a null pointer dereference will occur. Return value of function which returns null is dereferenced without checking
/src/mongo/db/s/shardsvr_check_metadata_consistency_participant_command.cpp:100: NULL_RETURNS 135525 Dereferencing a pointer that might be "nullptr" "*it" when calling "ns". (The dereference happens because this is a virtual function call.)