I found this while trying to write unit tests. Creating a local PigServer to test my LoadFunc caused a serialization of the PhysicalOperator class, which failed due to:
Caused by: java.io.NotSerializableException: org.apache.commons.logging.impl.Log4JCategoryLog
this is easily fixed by adding the transient keyword to the definition of log.
private final transient Log log = LogFactory.getLog(getClass());
on the 0.8 tag:
private transient Log log = LogFactory.getLog(getClass());