diff --git a/pkgs/development/ruby-modules/bundler-env/default.nix b/pkgs/development/ruby-modules/bundler-env/default.nix
index e82a6af0085..ba9ea5f3fa8 100644
--- a/pkgs/development/ruby-modules/bundler-env/default.nix
+++ b/pkgs/development/ruby-modules/bundler-env/default.nix
@@ -105,7 +105,9 @@ let
 
   gems = lib.flip lib.mapAttrs configuredGemset (name: attrs: buildGem name attrs);
 
-  maybeCopyAll = { usesGemspec ? false, ...}@main:
+  maybeCopyAll = main: if main == null then "" else copyIfUseGemspec main;
+
+  copyIfUseGemspec = { usesGemspec ? false, ...}@main:
   (if usesGemspec then ''
   cp -a ${gemdir}/* $out/
   '' else ""