private String findCommonPrefixOfVars(List<String> vars) {
String prefix = StringUtils.getCommonPrefix(vars.toArray(new String[vars.size()]));
// exclude trailing characters that should be part of a valid variable
// e.g. ["status-on", "status-off"] => "status-" (not "status-o")
return prefix.replaceAll("[a-zA-Z0-9]+\\z", "");
}
