[BUG] Elimination rules throw exceptions when setting both the operator and the variable(s)

[charlestian23]

Description

Consider the following example for Not Elimination:

When trying to set both not and A to any combination of true or false and then selecting "Not Elimination", the following happens:

And the following errors show up in the terminal:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at edu.rpi.legup.puzzle.shorttruthtable.rules.basic.DirectRule_Generic.checkRuleRawAt(DirectRule_Generic.java:43)
	at edu.rpi.legup.model.rules.DirectRule.checkRuleAt(DirectRule.java:82)
	at edu.rpi.legup.model.rules.DirectRule.checkRuleRaw(DirectRule.java:52)
	at edu.rpi.legup.model.rules.DirectRule.checkRule(DirectRule.java:37)
	at edu.rpi.legup.model.tree.TreeTransition.isCorrect(TreeTransition.java:337)
	at edu.rpi.legup.model.tree.TreeTransition.isContradictoryBranch(TreeTransition.java:221)
	at edu.rpi.legup.model.tree.TreeNode.isContradictoryBranch(TreeNode.java:36)
	at edu.rpi.legup.ui.proofeditorui.treeview.TreeNodeView.draw(TreeNodeView.java:77)
	at edu.rpi.legup.ui.proofeditorui.treeview.TreeView.redrawTree(TreeView.java:241)
	at edu.rpi.legup.ui.proofeditorui.treeview.TreeView.drawTree(TreeView.java:424)
	at edu.rpi.legup.ui.proofeditorui.treeview.TreeView.draw(TreeView.java:222)
	at edu.rpi.legup.ui.ZoomablePane.paint(ZoomablePane.java:28)
	at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
	at java.desktop/javax.swing.JComponent.paint(JComponent.java:1083)
	at java.desktop/javax.swing.JViewport.paint(JViewport.java:737)
	at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
	at java.desktop/javax.swing.JComponent.paint(JComponent.java:1083)
	at java.desktop/javax.swing.JComponent.paintToOffscreen(JComponent.java:5255)
	at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBufferedFPScales(RepaintManager.java:1707)
	at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1616)
	at java.desktop/javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1556)
	at java.desktop/javax.swing.RepaintManager.paint(RepaintManager.java:1323)
	at java.desktop/javax.swing.JComponent._paintImmediately(JComponent.java:5203)
	at java.desktop/javax.swing.JComponent.paintImmediately(JComponent.java:5013)
	at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:865)
	at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:848)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:848)
	at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:823)
	at java.desktop/javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:772)
	at java.desktop/javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1890)
	at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:313)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
	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)

Note that this also occurs for other elimination rules. See this screenshot for And Elimination:

Steps to Reproduce

1. Download BlankNot.zip
2. Unzip the file and open it in the proof editor
3. Set not and A to any combination of true or false
4. Attempt to justify this step with Not Elimination
5. See a new node not appear, and there should be an exception thrown in the terminal

Expected Behavior

A new node should appear with a red transition arrow, as this is not a valid application of Not Elimination.

Screenshots

No response

Puzzle Files

BlankNot.zip

Additional Context

Note that once this issue is fixed, the CannotSetBothAtOnceTest in src/test/java/puzzles/shorttruthtable/rules/NotEliminationTest.java should be uncommented. Additionally, it might be useful to generalize that test case for all Elimination rules.

[charlestian23]

Updated the description and title after doing some testing with Chase, this seems to be an issue across all Elimination rules.

[charlestian23]

Whoever works on this bug should uncomment the test case noted in #675.