Exception when xlsx-file continues after year

[ThatCraws]

When a time-tracking xlsx-file wraps from one year to the next, an exception will occur.

For example: When the file contains KW52 and after that KW01. The setCalendarWeek(int)-method is probably given the wrong week, when used in the dropdown-menu (dropdown-menu displays numbering in KWXX correctly though).

Exception

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "org.apache.poi.ss.usermodel.Sheet.getRow(int)" because "this.weekSheet" is null
        at de.esterlino.timeplater.worktimes.supplier.ExcelWorkWeekSupplier.setCalendarWeek(ExcelWorkWeekSupplier.java:89)
        at de.esterlino.timeplater.worktimes.supplier.ExcelWorkWeekSupplier.supplyWorkWeek(ExcelWorkWeekSupplier.java:74)
        at de.esterlino.timeplater.view.TimeplaterPanel$CalWeekComboBoxActionListener.actionPerformed(TimeplaterPanel.java:122)
        at java.desktop/javax.swing.JComboBox.fireActionEvent(JComboBox.java:1294)
        at java.desktop/javax.swing.JComboBox.setSelectedItem(JComboBox.java:619)
        at java.desktop/javax.swing.JComboBox.setSelectedIndex(JComboBox.java:654)
        at de.esterlino.timeplater.view.TimeplaterPanel.nextButtonActionPerformed(TimeplaterPanel.java:290)
        at de.esterlino.timeplater.view.TimeplaterPanel$3.actionPerformed(TimeplaterPanel.java:224)
        at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1972)
        at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2314)
        at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:407)
        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:6621)
        at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3398)
        at java.desktop/java.awt.Component.processEvent(Component.java:6386)
        at java.desktop/java.awt.Container.processEvent(Container.java:2266)
        at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:4996)
        at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2324)
        at java.desktop/java.awt.Component.dispatchEvent(Component.java:4828)
        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:4828)
        at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:775)
        at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:720)
        at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:714)
        at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
        at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:87)
        at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:98)
        at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:747)
        at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
        at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
        at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:87)
        at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:744)
        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)