message: Don't require DEVELOPER_DIR, but verify valid directory if set
diff: @@ -5,13 +5,12 @@ set -eo pipefail
  # Make sure SDKROOT variable is not set before building
  unset SDKROOT
  -# Make sure the DEVELOPER_DIR variable is set before building
  -if [[ -z "${DEVELOPER_DIR}" || ! -d "${DEVELOPER_DIR}" ]]; then
  - echo "error: DEVELOPER_DIR must be set to the xcode developer directory"
  +# If set, make sure the DEVELOPER_DIR variable is set to a valid directory
  +if [[ -n "${DEVELOPER_DIR}" && ! -d "${DEVELOPER_DIR}" ]]; then
  + echo "error: DEVELOPER_DIR is not a valid directory: ${DEVELOPER_DIR}"
  exit 1
  fi
  -
  SCRIPT="$(basename "${BASH_SOURCE[0]}")"
  VERSION="$(git describe)"
  