code: public static String getTagValue(Iterable<Tag> tags, String k) {
      Preconditions.checkNotNull(tags, "tags");
      Preconditions.checkNotNull(k, "key");
      for (Tag t : tags) {
        if (k.equals(t.key())) {
          return t.value();
        }
      }
      return null;
    }
docs: Returns the value associated with with a given key or null if no such key is present in the
  set of tags.
  
  @param tags
  Set of tags to search.
  @param k
  Key to search for.
  @return
  Value for the key or null if the key is not present.