FlightCrewSolution-null

[xhmywf]

Hello，now I can get a result quickly.Look the result:
GL0537→LSS0653, LSS0653→FU0721, FU0721→LSX0754, LSX0754→NH0818, NH0818→LSS0849, LSS0849→FU0918, FU0918→LSX0948, LSX0948→NH1013, NH1013→LH1044

But I want to transfer betweent two flights has some time space >=15 minutes,like:
GL0537→LSS0653, LSS0709→FU0738,

So I change this function below,but it work a long time and get no solution(FlightCrewSolution-null).What can I do?

    public long countInvalidConnections() {
        // TODO Cache this to improve example performance.
        // Especially useful for Constraint Streams, by which this is called multiple times per Employee.
        long count = 0L;
        FlightAssignment previousAssignment = null;
        for (FlightAssignment assignment : flightAssignmentSet) {
            if (previousAssignment != null
                    && (previousAssignment.getFlight().getArrivalAirport() != assignment.getFlight().getDepartureAirport()||assignment.getFlight().getDepartureUTCDateTime().compareTo(previousAssignment.getFlight().getArrivalUTCDateTime())<15)) {
                count++;
            }
            previousAssignment = assignment;
        }
        return count;
    }

Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: Failed writing outputSolutionFile (C:\Users\AppData\Local\Temp\970flights-1days.xlsx14207723011296920002.xlsx) for solution (FlightCrewSolution-null).
at org.optaplanner.examples.flightcrewscheduling.persistence.FlightCrewSchedulingXlsxFileIO.write(FlightCrewSchedulingXlsxFileIO.java:86)
at org.optaplanner.examples.flightcrewscheduling.persistence.FlightCrewSchedulingXlsxFileIO.write(FlightCrewSchedulingXlsxFileIO.java:1)
at org.optaplanner.examples.flightcrewscheduling.swingui.FlightCrewSchedulingPanel.lambda$0(FlightCrewSchedulingPanel.java:54)
at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1972)
at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2313)
at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
at java.desktop/java.awt.Component.processMouseEvent(Component.java:6626)
at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3389)
at java.desktop/java.awt.Component.processEvent(Component.java:6391)
at java.desktop/java.awt.Container.processEvent(Container.java:2266)
at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5001)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2324)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4833)
at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4948)
at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4575)
at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4516)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2310)
at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2780)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4833)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:773)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:722)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:716)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:97)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:746)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:744)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:743)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Caused by: java.lang.IllegalArgumentException: Merged region M3 must contain 2 or more cells
at org.apache.poi.xssf.usermodel.XSSFSheet.addMergedRegion(XSSFSheet.java:339)
at org.apache.poi.xssf.usermodel.XSSFSheet.addMergedRegion(XSSFSheet.java:304)
at org.optaplanner.examples.flightcrewscheduling.persistence.FlightCrewSchedulingXlsxFileIO$FlightCrewSchedulingXlsxWriter.writeEmployeesView(FlightCrewSchedulingXlsxFileIO.java:586)
at org.optaplanner.examples.flightcrewscheduling.persistence.FlightCrewSchedulingXlsxFileIO$FlightCrewSchedulingXlsxWriter.write(FlightCrewSchedulingXlsxFileIO.java:372)
at org.optaplanner.examples.flightcrewscheduling.persistence.FlightCrewSchedulingXlsxFileIO.write(FlightCrewSchedulingXlsxFileIO.java:83)
... 37 more

970flights-1days.xlsx