StringIndexOutOfBoundsException when a fact is in default package

Assuming you have a rule base for which you have defined shadow proxy excludes.
If you insert a fact which class is in default package, a StringIndexOutOfBoundsException is raised by RuleBaseConfiguration#isShadowed()

java.lang.StringIndexOutOfBoundsException: String index out of range: -1
at java.lang.String.substring(String.java:1768)
at org.drools.RuleBaseConfiguration.isShadowed(RuleBaseConfiguration.java:546)
at org.drools.reteoo.Rete$ClassObjectTypeConf.defineShadowProxyData(Rete.java:486)
at org.drools.reteoo.Rete$ClassObjectTypeConf.<init>(Rete.java:468)
at org.drools.reteoo.Rete.assertObject(Rete.java:152)
at org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:192)
at org.drools.reteoo.ReteooWorkingMemory.doInsert(ReteooWorkingMemory.java:71)
at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:911)
at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:883)
at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:704)
..........

Problem comes from this line (RuleBaseConfiguration.java:546):
String qualifiedNamespace = className.substring( 0,
className.lastIndexOf( '.' ) ).trim(); // => default package => no '.' => exception

This can typically happen when trying to insert JDKProxies into the working memory for test purpose (EasyMock use such proxies).

The issue only appears if you have defined shadow proxy excludes.