Further improve processing of null arguments in remote endpoint (followup to r1632625):
1) Document IllegalArgumentException in javadoc
2) Handle null arguments in sendObject() methods to throw IllegalArgumentException instead of NPE.


git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1632965 13f79535-47bb-0310-9956-ffa450edef68