Merge pull request #13417 from ghalliday/issue23599

HPCC-23599 Allow the legacy configuration filename to be omitted

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>

system/jlib/jptree.cpp

@@ -7972,7 +7972,7 @@ jlib_decl IPropertyTree * loadConfiguration(const char * defaultYaml, const char
     }
     else
     {
-        if (checkFileExists(legacyFilename))
+        if (legacyFilename && checkFileExists(legacyFilename))
             delta.setown(createPTreeFromXMLFile(legacyFilename, ipt_caseInsensitive));
 
         if (delta && mapper)