Pull request #727: Adding immutable guava collections.

Merge in MC/connect from bugfix/ROCKSOLID-11324-switch-xstream-to-use-allowlist-instead-of-denylist to 4.4.x

* commit '63139fe9ecb39a3a15bf4f366164d25a0323dc5f':
  Adding immutable guava collections.

Author: narupley

donkey/src/main/java/com/mirth/connect/donkey/util/xstream/XStreamSerializer.java

@@ -71,7 +71,8 @@ protected MapperWrapper wrapMapper(MapperWrapper next) {
                 "com.mirth.connect.plugins.**", "com.mirth.connect.util.**",
                 "com.mirth.connect.userutil.**", "com.mirth.connect.donkey.model.**",
                 "com.mirth.connect.donkey.util.**", "com.mirth.connect.jsonbuilder.**",
-                "com.mirth.generator.model.**", "java.security.**" });
+                "com.mirth.generator.model.**", "java.security.**",
+                "com.google.common.collect.Immutable**" });
 
         if (classLoader != null) {
             xstream.setClassLoader(classLoader);