"ERROR: Can not prepare request: null" on deletion

[Alvin Peng]

create table USER(
USER_ID varchar2(32) not null,
USER_NAME varchar2(32) not null);

alter table USER add constraint PK_USER primary key(USER_ID);

create table ACTION_RECORD(
ACTION_ID varchar2(32) not null,
USER_ID varchar2(32) not null);

alter table ACTION_RECORD add constraint PK_ACTION primary key(ACTION_ID);
alter table ACTION_RECORD add constraint FK_USER foreign key(USER_ID) references USER(USER_ID);

test2rep=> delete from user where user_id=1;
ERROR: Can not prepare request: null

=========
In SqlModifyTable.java:

public void prepare() throws Exception {
...
            tempTable = createTempTableMetadata(getTargetTable(),
                    getColumnsInvolved());
            dataSource = prepareDataSource(targetTable, tempTable);
            for (IConstraintChecker validator : validators) {
                validator.setTempTable(tempTable);
                validator.prepare();
            }
...
}

The tempTable is null, so validator.prepare(); throws the exception.