in
src/j2ee/persistence/src/org/netbeans/modules/j2ee/persistence/wizard/fromdb/JavaPersistenceGenerator.java
line 392 you have :
                            CMPMappingModel.JoinTableColumnMapping joinColumnMap
= dbMappings.getJoinTableColumnMppings().get(role.getFieldName());

however this call is returning null for joinColumnMap and hence an NPE is raised
in the following code. Part of the reason is that in debug i can see that
role.getFieldName() is returning fieldName but with an indice of 1 like
"fiedName1". This is caused (i think) by the fact that :

1) in buildCMPSet() of DbSchemaEjbGenerator addJoinTable was called *before* the
call to makeBeansUnique. so addJoinTable innocently adds the old mapping by
calling
roleAHelper.getCMPMapping().getJoinTableColumnMppings().put(role{A,B}Cmr,
joinColMap{A,B})
2) makeBeansUnique adds indices to all the beans. But the mapping
(getJoinTableColumnMppings()) still contains the old names of the beans before
they were made unique. So obviously
dbMappings.getJoinTableColumnMppings().get(role.getFieldName()) returns null.

This should be fairly simple to fix for someone who is familiar with the code.