@Override public final String getHeaderField(String fieldName) {
    try {
      return fieldName == null
          ? StatusLine.get(getResponse().getResponse()).toString()
          : getHeaders().get(fieldName);
    } catch (IOException e) {
      return null;
    }
  }
Returns the value of the field corresponding to the {@code fieldName}, or
null if there is no such field. If the field has multiple values, the
last value is returned.
gateway/platforms/servlet/src/main/java/io/apiman/gateway/platforms/servlet/connectors/ok/HttpURLConnectionImpl.java