SQLGrammarException in getTasksAssignedAsPotentialOwner executed via Remote API

Description of problem:

I use BPMS 6.0.2.ER3 with PostgreSQL 9.2 but I assume that on other databases could be the problem as well. Although, it does work with the default H2 database.

When I execute getTasksAssignedAsPotentialOwner operation in the JMS TaskService, I get:

org.kie.services.client.api.command.exception.RemoteApiException: SQLGrammarException thrown with message 'could not extract ResultSet'
at org.kie.services.client.api.command.AbstractRemoteCommandObject.executeJmsCommand(AbstractRemoteCommandObject.java:358)
at org.kie.services.client.api.command.AbstractRemoteCommandObject.execute(AbstractRemoteCommandObject.java:126)
at org.jbpm.services.task.impl.command.CommandBasedTaskService.getTasksAssignedAsPotentialOwner(CommandBasedTaskService.java:185)

I attached the part of server log where is the full stacktrace of the exception. :

org.postgresql.util.PSQLException: ERROR: syntax error at or near ")"
Position: 1167
.....

Version-Release number of selected component (if applicable):

How reproducible:

In your test case, it is not needed to have some existing task. In such scenario the operation should return empty list but in this case it returns the exception.

It should be enough to run this code:
List<TaskSummary> tasksForTestUser = taskService.getTasksAssignedAsPotentialOwner("testuser", "en-UK");

and the list should be empty.

Steps to Reproduce:
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Actual results:

Expected results:

Additional info: