Fix pname to ename propagation if null

pkgs/build-support/emacs/melpa.nix

@@ -13,7 +13,7 @@ with lib;
   /*
     ename: Original Emacs package name, possibly containing special symbols.
   */
-, ename ? pname
+, ename ? null
 , version
 , recipe
 , meta ? {}
@@ -30,6 +30,11 @@ in
 
 import ./generic.nix { inherit lib stdenv emacs texinfo; } ({
 
+  ename =
+    if isNull(ename)
+    then pname
+    else ename;
+
   melpa = fetchFromGitHub {
     owner = "melpa";
     repo = "melpa";