Bulk insert of data with nullable UNIQUE constraint fails to detect duplicates

The constraint can be subverted using e.g. call SYSCS_UTIL.SYSCS_IMPORT_TABLE, cf. the below script:

test.sql:
connect 'jdbc:derby:memory:wombat;create=true';
create table t_unique_nullable(i int, j int, constraint c_unique_n unique);
call SYSCS_UTIL.SYSCS_IMPORT_TABLE ('APP', 'T_UNIQUE_NULLABLE', 'test.data', '|', '`', null, 1);
select * from t_unique_nullable;
create table t_unique(i int not null, j int, constraint c_unique unique);
call SYSCS_UTIL.SYSCS_IMPORT_TABLE ('APP', 'T_UNIQUE', 'test.data', '|', '`', null, 1);

which fails in the second import, but not the first one, given this data file:

test.data
1 | 1
1 | 1
2 | 2

run:
ij version 10.11
ij> connect 'jdbc:derby:memory:wombat;create=true';
ij> autocommit off;
ij> create table t_unique_nullable(i int, j int, constraint c_unique_n unique);
0 rows inserted/updated/deleted
ij> call SYSCS_UTIL.SYSCS_IMPORT_TABLE ('APP', 'T_UNIQUE_NULLABLE', 'test.data',
'|', '`', null, 1);
0 rows inserted/updated/deleted
ij> select * from t_unique_nullable;
I |J
-----------------------
1 |1
1 |1
2 |2

3 rows selected
ij> create table t_unique(i int not null, j int, constraint c_unique unique);
0 rows inserted/updated/deleted
ij> call SYSCS_UTIL.SYSCS_IMPORT_TABLE ('APP', 'T_UNIQUE', 'test.data',
'|', '`', null, 1);
ERROR XIE0R: Import error on line 2 of file test.data: The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'C_UNIQUE' defined on 'T_UNIQUE'.
java.sql.SQLException: Import error on line 2 of file test.data: The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'C_UNIQUE' defined on 'T_UNIQUE'.
at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:103)
at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Util.java:137)
at org.apache.derby.impl.jdbc.Util.seeNextException(Util.java:310)
at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(TransactionResourceImpl.java:431)
at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(TransactionResourceImpl.java:353)
at org.apache.derby.impl.jdbc.EmbedConnection.handleException(EmbedConnection.java:2395)
at org.apache.derby.impl.jdbc.ConnectionChild.handleException(ConnectionChild.java:82)
at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1429)
at org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:704)
at org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:631)
at org.apache.derby.impl.tools.ij.ij.executeImmediate(ij.java:367)
at org.apache.derby.impl.tools.ij.utilMain.doCatch(utilMain.java:527)
at org.apache.derby.impl.tools.ij.utilMain.runScriptGuts(utilMain.java:369)
at org.apache.derby.impl.tools.ij.utilMain.go(utilMain.java:245)
at org.apache.derby.impl.tools.ij.Main.go(Main.java:229)
at org.apache.derby.impl.tools.ij.Main.mainCore(Main.java:184)
at org.apache.derby.impl.tools.ij.Main.main(Main.java:75)
at org.apache.derby.tools.ij.main(ij.java:59)
at ij.Ij.main(Ij.java:19)
Caused by: java.sql.SQLException: Import error on line 2 of file test.data: The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'C_UNIQUE' defined on 'T_UNIQUE'.
at org.apache.derby.impl.jdbc.SQLExceptionFactory.wrapArgsForTransportAcrossDRDA(SQLExceptionFactory.java:138)
at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:73)
... 18 more
Caused by: java.sql.SQLException: The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'C_UNIQUE' defined on 'T_UNIQUE'.
at org.apache.derby.impl.jdbc.SQLExceptionFactory.wrapArgsForTransportAcrossDRDA(SQLExceptionFactory.java:138)
at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:73)
at org.apache.derby.impl.jdbc.Util.generateCsSQLException(Util.java:288)
at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(TransactionResourceImpl.java:424)
at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(TransactionResourceImpl.java:353)
at org.apache.derby.impl.jdbc.EmbedConnection.handleException(EmbedConnection.java:2395)
at org.apache.derby.impl.jdbc.ConnectionChild.handleException(ConnectionChild.java:82)
at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1429)
at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeStatement(EmbedPreparedStatement.java:1709)
at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeLargeUpdate(EmbedPreparedStatement.java:320)
at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeUpdate(EmbedPreparedStatement.java:309)
at org.apache.derby.impl.load.Import.performImport(Import.java:289)
at org.apache.derby.impl.load.Import.importTable(Import.java:126)
at org.apache.derby.catalog.SystemProcedures.SYSCS_IMPORT_TABLE(SystemProcedures.java:1571)
at org.apache.derby.exe.ac4d3680a5x0141x937dxb945x000006a67bf04.g0(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.derby.impl.services.reflect.ReflectMethod.invoke(ReflectMethod.java:46)
at org.apache.derby.impl.sql.execute.CallStatementResultSet.open(CallStatementResultSet.java:75)
at org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(GenericPreparedStatement.java:438)
at org.apache.derby.impl.sql.GenericPreparedStatement.execute(GenericPreparedStatement.java:319)
at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1337)
... 11 more
Caused by: ERROR 23505: The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'C_UNIQUE' defined on 'T_UNIQUE'.
at org.apache.derby.iapi.error.StandardException.newException(StandardException.java:265)
at org.apache.derby.iapi.error.StandardException.newException(StandardException.java:260)
at org.apache.derby.impl.sql.execute.UniqueIndexSortObserver.insertDuplicateKey(UniqueIndexSortObserver.java:72)
at org.apache.derby.impl.store.access.sort.SortBuffer.insert(SortBuffer.java:245)
at org.apache.derby.impl.store.access.sort.MergeInserter.insert(MergeInserter.java:103)
at org.apache.derby.impl.sql.execute.InsertResultSet.changedRow(InsertResultSet.java:234)
at org.apache.derby.impl.sql.execute.NoPutResultSetImpl.rowLocation(NoPutResultSetImpl.java:285)
at org.apache.derby.impl.store.access.heap.HeapController.load(HeapController.java:450)
at org.apache.derby.impl.store.access.heap.Heap.load(Heap.java:651)
at org.apache.derby.impl.store.access.RAMTransaction.loadConglomerate(RAMTransaction.java:1216)
at org.apache.derby.impl.store.access.RAMTransaction.recreateAndLoadConglomerate(RAMTransaction.java:885)
at org.apache.derby.impl.store.access.RAMTransaction.createAndLoadConglomerate(RAMTransaction.java:844)
at org.apache.derby.impl.sql.execute.InsertResultSet.bulkInsertCore(InsertResultSet.java:1331)
at org.apache.derby.impl.sql.execute.InsertResultSet.open(InsertResultSet.java:467)
at org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(GenericPreparedStatement.java:438)
at org.apache.derby.impl.sql.GenericPreparedStatement.execute(GenericPreparedStatement.java:319)
at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1337)
... 27 more
ERROR 23505: The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'C_UNIQUE' defined on 'T_UNIQUE'.
java.sql.SQLIntegrityConstraintViolationException: The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'C_UNIQUE' defined on 'T_UNIQUE'.
at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:83)
at org.apache.derby.impl.jdbc.Util.generateCsSQLException(Util.java:288)
at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(TransactionResourceImpl.java:424)
at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(TransactionResourceImpl.java:353)
at org.apache.derby.impl.jdbc.EmbedConnection.handleException(EmbedConnection.java:2395)
at org.apache.derby.impl.jdbc.ConnectionChild.handleException(ConnectionChild.java:82)
at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1429)
at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeStatement(EmbedPreparedStatement.java:1709)
at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeLargeUpdate(EmbedPreparedStatement.java:320)
at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeUpdate(EmbedPreparedStatement.java:309)
at org.apache.derby.impl.load.Import.performImport(Import.java:289)
at org.apache.derby.impl.load.Import.importTable(Import.java:126)
at org.apache.derby.catalog.SystemProcedures.SYSCS_IMPORT_TABLE(SystemProcedures.java:1571)
at org.apache.derby.exe.ac4d3680a5x0141x937dxb945x000006a67bf04.g0(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.derby.impl.services.reflect.ReflectMethod.invoke(ReflectMethod.java:46)
at org.apache.derby.impl.sql.execute.CallStatementResultSet.open(CallStatementResultSet.java:75)
at org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(GenericPreparedStatement.java:438)
at org.apache.derby.impl.sql.GenericPreparedStatement.execute(GenericPreparedStatement.java:319)
at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1337)
at org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:704)
at org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:631)
at org.apache.derby.impl.tools.ij.ij.executeImmediate(ij.java:367)
at org.apache.derby.impl.tools.ij.utilMain.doCatch(utilMain.java:527)
at org.apache.derby.impl.tools.ij.utilMain.runScriptGuts(utilMain.java:369)
at org.apache.derby.impl.tools.ij.utilMain.go(utilMain.java:245)
at org.apache.derby.impl.tools.ij.Main.go(Main.java:229)
at org.apache.derby.impl.tools.ij.Main.mainCore(Main.java:184)
at org.apache.derby.impl.tools.ij.Main.main(Main.java:75)
at org.apache.derby.tools.ij.main(ij.java:59)
at ij.Ij.main(Ij.java:19)
Caused by: java.sql.SQLException: The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'C_UNIQUE' defined on 'T_UNIQUE'.
at org.apache.derby.impl.jdbc.SQLExceptionFactory.wrapArgsForTransportAcrossDRDA(SQLExceptionFactory.java:138)
at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:73)
... 33 more
Caused by: ERROR 23505: The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint or unique index identified by 'C_UNIQUE' defined on 'T_UNIQUE'.
at org.apache.derby.iapi.error.StandardException.newException(StandardException.java:265)
at org.apache.derby.iapi.error.StandardException.newException(StandardException.java:260)
at org.apache.derby.impl.sql.execute.UniqueIndexSortObserver.insertDuplicateKey(UniqueIndexSortObserver.java:72)
at org.apache.derby.impl.store.access.sort.SortBuffer.insert(SortBuffer.java:245)
at org.apache.derby.impl.store.access.sort.MergeInserter.insert(MergeInserter.java:103)
at org.apache.derby.impl.sql.execute.InsertResultSet.changedRow(InsertResultSet.java:234)
at org.apache.derby.impl.sql.execute.NoPutResultSetImpl.rowLocation(NoPutResultSetImpl.java:285)
at org.apache.derby.impl.store.access.heap.HeapController.load(HeapController.java:450)
at org.apache.derby.impl.store.access.heap.Heap.load(Heap.java:651)
at org.apache.derby.impl.store.access.RAMTransaction.loadConglomerate(RAMTransaction.java:1216)
at org.apache.derby.impl.store.access.RAMTransaction.recreateAndLoadConglomerate(RAMTransaction.java:885)
at org.apache.derby.impl.store.access.RAMTransaction.createAndLoadConglomerate(RAMTransaction.java:844)
at org.apache.derby.impl.sql.execute.InsertResultSet.bulkInsertCore(InsertResultSet.java:1331)
at org.apache.derby.impl.sql.execute.InsertResultSet.open(InsertResultSet.java:467)
at org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(GenericPreparedStatement.java:438)
at org.apache.derby.impl.sql.GenericPreparedStatement.execute(GenericPreparedStatement.java:319)
at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1337)
... 27 more
ij> BUILD SUCCESSFUL (total time: 2 seconds)