private Charset getCharset(String contentTypeValue) {
    val matcher = CHARSET_PATTERN.matcher(contentTypeValue);
    return matcher.find() ? Charset.forName(matcher.group(1)) : UTF_8;
  }
Returns {@link ContentProcessor} for specific {@link ContentType}.

@param type a type for content processor search.
@return {@link ContentProcessor} instance for specified type or null.
form/src/main/java/feign/form/FormEncoder.java