Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "java.lang.Long.longValue()" because the return value of "java.util.HashMap.get(Object)" is null
	at LineGraph$1.compare(LineGraph.java:60)
	at LineGraph$1.compare(LineGraph.java:58)
	at java.base/java.util.TimSort.binarySort(TimSort.java:296)
	at java.base/java.util.TimSort.sort(TimSort.java:239)
	at java.base/java.util.Arrays.sort(Arrays.java:1308)
	at java.base/java.util.ArrayList.sort(ArrayList.java:1804)
	at java.base/java.util.Collections.sort(Collections.java:178)
	at LineGraph.sortYearly(LineGraph.java:58)
	at LineGraph.monthly(LineGraph.java:76)
	at LineGraph.paintComponent(LineGraph.java:54)
	at java.desktop/javax.swing.JComponent.paint(JComponent.java:1128)
	at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:961)
	at java.desktop/javax.swing.JComponent.paint(JComponent.java:1137)
	at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:961)
	at java.desktop/javax.swing.JComponent.paint(JComponent.java:1137)
	at java.desktop/javax.swing.JLayeredPane.paint(JLayeredPane.java:586)
	at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:961)
	at java.desktop/javax.swing.JComponent.paintToOffscreen(JComponent.java:5325)
	at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBufferedImpl(RepaintManager.java:1656)
	at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1631)
	at java.desktop/javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1569)
	at java.desktop/javax.swing.RepaintManager.paint(RepaintManager.java:1336)
	at java.desktop/javax.swing.JComponent.paint(JComponent.java:1114)
	at java.desktop/java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
	at java.desktop/sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:75)
	at java.desktop/sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:112)
	at java.desktop/java.awt.Container.paint(Container.java:2005)
	at java.desktop/java.awt.Window.paint(Window.java:3959)
	at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:889)
	at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:861)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:87)
	at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:861)
	at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:834)
	at java.desktop/javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:784)
	at java.desktop/javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1897)
	at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:318)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:773)
	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.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
	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)