/subsystem=jpa:write-attribute(name=default-datasource, value="java:jboss/datasources/ExampleDS")

10:55:11,358 ERROR [org.jboss.as.controller] (HttpManagementService-threads - 13) JBAS014612: Operation ("write-attribute") failed - address: ([("subsystem" => "jpa")]): java.lang.NullPointerException
	at org.jboss.as.jpa.subsystem.JPADefaultDatasourceWriteHandler.applyUpdateToRuntime(JPADefaultDatasourceWriteHandler.java:39) [jboss-as-jpa-7.1.0.CR1-SNAPSHOT.jar:]
	at org.jboss.as.controller.AbstractWriteAttributeHandler$1.execute(AbstractWriteAttributeHandler.java:113) [jboss-as-controller-7.1.0.CR1-SNAPSHOT.jar:]
	at org.jboss.as.controller.AbstractOperationContext.executeStep(AbstractOperationContext.java:322) [jboss-as-controller-7.1.0.CR1-SNAPSHOT.jar:]
	at org.jboss.as.controller.AbstractOperationContext.doCompleteStep(AbstractOperationContext.java:216) [jboss-as-controller-7.1.0.CR1-SNAPSHOT.jar:]
	at org.jboss.as.controller.AbstractOperationContext.completeStep(AbstractOperationContext.java:152) [jboss-as-controller-7.1.0.CR1-SNAPSHOT.jar:]
	at org.jboss.as.controller.AbstractWriteAttributeHandler.execute(AbstractWriteAttributeHandler.java:135) [jboss-as-controller-7.1.0.CR1-SNAPSHOT.jar:]