message: Uberenv should only 'activate' python packages that exist
  Otherwise, spack prints out an error message.
diff: @@ -393,8 +393,11 @@ def main():
  return res
  if "spack_activate" in project_opts:
  for pkg_name in project_opts["spack_activate"]:
  + # Only attempt to activate packages that were actually built
  + find_cmd = "spack/bin/spack find | grep " + pkg_name
  activate_cmd = "spack/bin/spack activate " + pkg_name
  - sexe(activate_cmd, echo=True)
  + conditional_activate_cmd = "{} && {}".format(find_cmd, activate_cmd)
  + sexe(conditional_activate_cmd, echo=True)
  return res
  if __name__ == "__main__":
  