anchor.diff:  let
     darwinChanges = ''
       if test -e /run/current-system/darwin-changes; then
  -      darwinChanges=$(grep -v -f /run/current-system/darwin-changes $systemConfig/darwin-changes 2> /dev/null)
  +      darwinChanges=$(grep -v -f /run/current-system/darwin-changes $systemConfig/darwin-changes 2> /dev/null) || true
         if test -n "$darwinChanges"; then
           echo >&2
           echo "[1;1mCHANGELOG[0m" >&2
  
positive.code:   '';
  
    buildUsers = optionalString config.services.nix-daemon.enable ''
      buildUser=$(dscl . -read /Groups/nixbld GroupMembership 2>&1 | awk '/^GroupMembership: / {print $2}')
      if [ -z $buildUser ]; then
          echo "[1;31merror: Using the nix-daemon requires build users, aborting activation[0m" >&2
          echo "Create the build users or disable the daemon:" >&2
  
negative.code:   config = {
  
      system.activationScripts.checks.text = ''
        ${darwinChanges}
        ${buildUsers}
        ${nixPath}
  