When calling `ResultSet.getMetaData()` on a (closed) result set of a (closed) connection a NPE can occur. Instead it should throw an exception that the result set is closed.

Exception below is in 2.2.12, Jaybird 3 has a similar problem, but it does not throw an NullPointerException.

java.lang .NullPointerException
    at org.firebirdsql.jdbc.AbstractConnection.getDatabaseParameterBuffer(AbstractConnection.java:224)
    at org.firebirdsql.jdbc.FBResultSetMetaData.<init>(FBResultSetMetaData.java:61)
    at org.firebirdsql.jdbc.AbstractResultSet.getMetaData(AbstractResultSet.java:1025)
    at com.borland.dx.sql.dataset.RuntimeMetaData.a(Unknown Source)
    at com.borland.dx.sql.dataset.JdbcProvider.b(Unknown Source)
    at com.borland.dx.sql.dataset.JdbcProvider.provideData(Unknown Source)
    at com.borland.dx.dataset.StorageDataSet.refresh(Unknown Source)
    at com.borland.dx.sql.dataset.QueryDataSet.refresh(Unknown Source)

Exception in Jaybird 3.0.0-beta-2 is:

java.sql.SQLException: no transaction for request [SQLState:25000, ISC error code:335544363]
at org.firebirdsql.gds.ng.FbExceptionBuilder$Type$1.createSQLException(FbExceptionBuilder.java:498)
at org.firebirdsql.gds.ng.FbExceptionBuilder$ExceptionInformation.toSQLException(FbExceptionBuilder.java:454)
at org.firebirdsql.gds.ng.FbExceptionBuilder.toSQLException(FbExceptionBuilder.java:218)
at org.firebirdsql.jdbc.FBConnection.getGDSHelper(FBConnection.java:1433)
at org.firebirdsql.jdbc.FBResultSetMetaData.isColumnLabelForName(FBResultSetMetaData.java:75)
at org.firebirdsql.jdbc.FBResultSetMetaData.<init>(FBResultSetMetaData.java:64)
at org.firebirdsql.jdbc.AbstractResultSet.getMetaData(AbstractResultSet.java:1098)