Work on Concurrency view

src/taste-concurrency_view.ads

@@ -35,7 +35,7 @@ package TASTE.Concurrency_View is
          Name            : Unbounded_String;
          Provided        : Protected_Block_PIs.Map;
          Required        : Interfaces_Maps.Map;
-         Calling_Threads : String_Vectors.Vector;
+         Calling_Threads : String_Sets.Set;
          Node            : Option_Node.Option;
       end record;
 

src/taste-parser_utils.adb

@@ -125,7 +125,7 @@ package body TASTE.Parser_Utils is
       if Result.Version then
          raise Exit_From_Command_Line;
       end if;
-      if Result.Output_Dir.all'Length = 0 then
+      if Result.Output_Dir = null or else Result.Output_Dir.all'Length = 0 then
          Result.Output_Dir := new String'(".");
       end if;
    end Parse_Command_Line;