SecurityWrapperResponse.setHeader does not handle nulls

[ThrawnCA]

Describe the bug

Passing null to either the name or value parameters of SecurityWrapperResponse.setHeader will result in a NullPointerException (within StringUtilities.stripControls). This is almost always undesired behaviour, and contrary to the latest Servlet specification, which states how null values should behave (null header name is a no-op, null header value is a deletion).

Specify what ESAPI version(s) you are experiencing this bug in

2.7.0.0

To Reproduce

1. Create an application that wraps the request and response in SecurityRequestWrapper.
2. Attempt to delete a header using setHeader("myHeader", null)
3. NullPointerException

Expected behavior

Null values should be ignored by ESAPI and gracefully passed to regular code.