private String createKeyValuePairFromCollection(String key, Object values, Charset charset) {
    val collection = (Collection<?>) values;
    val array = collection.toArray(new Object[0]);
    return createKeyValuePairFromArray(key, array, charset);
  }
An URL encoded form content processor.

@author Artem Labazin
form/src/main/java/feign/form/UrlencodedFormContentProcessor.java