stdenv/check-meta: exit early if no meta defined

  # Along with a boolean flag for each reason

  checkValidity =

    attrs:

    if !attrs ? meta then

      null

    else

    # Check meta attribute types first, to make sure it is always called even when there are other issues

    # Note that this is not a full type check and functions below still need to by careful about their inputs!

    if checkMeta && metaInvalid (attrs.meta or { }) then

    if checkMeta && metaInvalid attrs.meta then

      {

        reason = "unknown-meta";

        msg = "has an invalid meta attrset:${