NullPointerException in DefaultUrlHelper

In the method DefaultUrlHelper.buildParametersString(...) a NullPointerException occurs whenever an array or iterable parameter containing null elements is passed.

The problem seems to be lines 214 and 244, which look the same:

link.append(buildParameterSubstring(name, paramValue.toString()));

For null parameters an empty string is written to the url:

value != null ? value.toString() : StringUtils.EMPTY

A fix would be to check paramValue for null as well, thus allowing arrays or iterables to contain null elements.