empty string variable for proxyList should be handled

Property proxyList without specified value should be handled as follows: there are no proxies.

<property name="proxyList"></property>

This could be done by replacing line 389 of MCMPUtils.java:

if (proxyList == null) return Collections.emptyList();

to

if (proxyList == null || proxyList.length() == 0) return Collections.emptyList();

This bug is related to MODCLUSTER-36. If we give an empty default value JBoss fails with exception:

2009-01-09 18:13:11,505 ERROR [org.apache.tomcat.util.modeler.BaseModelMBean] (main) Exception invoking method start
java.lang.IllegalArgumentException: [address] is null