Index: src/natools-s_expressions-interpreters.ads
==================================================================
--- src/natools-s_expressions-interpreters.ads
+++ src/natools-s_expressions-interpreters.ads
@@ -56,10 +56,15 @@
       Context : in Shared_Context;
       Cmd : in out Lockable.Descriptor'Class)
      is null;
       --  Execute a single command with arguments
 
+
+   type Null_Command is new Command with null record;
+
+   Do_Nothing : Null_Command := Null_Command'(null record);
+
 
    type Interpreter is new Command with private;
 
    procedure Add_Command
      (Self : in out Interpreter;