code: public static Tag<String> fromString(String tagKeyValue) {
      List<String> splitKeyValue = Splitter.on(KEY_VALUE_SEPARATOR).limit(2).omitEmptyStrings().splitToList(tagKeyValue);
      if(splitKeyValue.size() == 2) {
        return new Tag<>(splitKeyValue.get(0), splitKeyValue.get(1));
      } else {
        return null;
      }
    }
docs: Reverse of Tag.toString(). Parses a string of the form "key:value" into a {@link Tag}.
  
  <p>
  If there are multiple ":" in the input string, the key will be the substring up to the first ":", and the
  value will be the substring after the first ":".
  </p>
  
  @param tagKeyValue String of the form "key:value".
  @return {@link org.apache.gobblin.metrics.Tag} parsed from input.