code: public Format getFormatByArgumentName(String argumentName) {
          if (cachedFormatters == null) {
              return null;
          }
          int argNumber = MessagePattern.validateArgumentName(argumentName);
          if (argNumber < MessagePattern.ARG_NAME_NOT_NUMBER) {
              return null;
          }
          for (int partIndex = 0; (partIndex = nextTopLevelArgStart(partIndex)) >= 0;) {
              if (argNameMatches(partIndex + 1, argumentName, argNumber)) {
                  return cachedFormatters.get(partIndex);
              }
          }
          return null;
      }
docs: <strong>[icu]</strong> Returns the first top-level format associated with the given argument name.
  For more details, see {@link #setFormatByArgumentName(String, Format)}.
  @param argumentName The name of the desired argument.
  @return the Format associated with the name, or null if there isn't one.