code: private static void logVersionWarnings(String label1, String version1, String label2, String version2) {
  		if (version1 == null) {
  			if (version2 != null) {
  				warning(null, "Unknown version", " for {}, version for {} is '{}'", new Object[] { label1, label2,
  						version2 });
  			}
  		} else {
  			if (version2 == null) {
  				warning(null, "Unknown version", " for {}, version for {} is '{}'", new Object[] { label2, label1,
  						version1 });
  			} else if (!version1.equals(version2)) {
  				warning(null, "Mismatched versions", ": {} is '{}', while {} is '{}'", new Object[] { label1, version1,
  						label2, version2 });
  			}
  		}
  	}
docs: Log error information