code: protected String getAppliedCharset(Map<String, String> headers) {
          String encoding;
          if (headers != null && (encoding = headers.get("charset")) != null) {
              return encoding;
          }
          return "US-ASCII"; 
      }
docs: Gets the charset that should be used to encode the {@link DataUrl}
  @param headers Headers map
  @return Applied charset, never {@code null}