CachedEntityStatistics depends on @GeneratedValue which is not supported in Oracle by default unless special trigger and OracleDictionary setting is implemented.
Otherwise, the following similar exception will be observed.
Caused by: org.apache.openjpa.lib.jdbc.ReportingSQLException: ORA-01400: cannot insert NULL into ("JPAUSER"."CACHEDENTITYSTATISTICS"."ID")
SInce TestStatistics, the test case uses CachedEntityStatistics, is not testing GeneratedValue per se, will remove the annotation and implement a simple id assignment in CachedEntityStatistics class.