HSQL Database Engine 1.8.1
java.lang.NullPointerException
at org.hsqldb.Session.execute(Session.java:881)
at org.hsqldb.jdbc.jdbcPreparedStatement.<init>(jdbcPreparedStatement.java:1830)
at org.hsqldb.jdbc.jdbcConnection.prepareStatement(jdbcConnection.java:1513)
I think, HSQLDB should throw a meaningful exception that cane be recognized as "datafile is locked".
Yes, it would be a good idea. We are now focused on version 2.x but will update version 1.8.x if we find an easy-to-add enhancement.
Version 1.8.x was never updated since the ticket.