I'm a couple days wiser now in the ways of type mapping in Axis, so I thought I'd post the answer to my own question in case someone else runs into the same problem.
Quick recap: my service class has functions which take as parameters and return arrays of java.util.Map. Client calls to these functions resulted in null pointer exceptions on the server in alpha-3 and nightly builds between 1/26 and 1/30. The solution: add the following to the service deployment descriptor: <typeMapping qname="ns1:Map" xmlns:ns1="http://xml.apache.org/xml-soap"; languageSpecificType="java:java.util.Map" serializer="org.apache.axis.encoding.ser.MapSerializerFactory" deserialiser="org.apache.axis.encoding.ser.MapDeserializerFactory" /> Note that these factory packages will work with 1/30 builds or later; if you're still using alpha-3, use "org.apache.axis.encoding". I'm still of the opinion that I shouldn't need to specify the serializer for Map when Hashtable and HashMap are intriniscally supported. This is more of a quibble than a serious problem, though. p.
