Null pointer in ParticleMathMapping.refreshMathDescription

[danv61]

We try to access forward and reverse rate of a mass action stochastic function which may be null.
Happens in ParticleMathMapping.refreshMathDescription() around line 732
Here's the significant part of the code:

				StochasticFunction stochasticFunction = StochasticTransformer.transformToStochastic(reactionStep);
				if (stochasticFunction instanceof MassActionStochasticFunction)
				{
					maFunc = (MassActionStochasticFunction)stochasticFunction;
				}
				if ((maFunc.forwardRate() == null && maFunc.reverseRate() == null))   <-- maFunc may be null here

Comes from VCell Support bug report, here's a small part of a (huge) stack trace:

Sent: Wednesday, April 8, 2026 8:13:56 AM (UTC-05:00) Eastern Time (US & Canada)
To: Virtual Cell Support
Subject: VCell Support sent through Contact-Us
Log file content:
NetworkFreePanel: SimContext@7f231fc9([Name(non spatial determintic), key(308949947), Owner(Sybren(304037797)), GroupAccess(Private), BranchPointRef(null), BranchID(308044382), Flag(Current), Date(02-Apr-2026 08:01:57), Annot(Length\u003d26)]), appendToConsole
Clean
NetworkFreePanel: SimContext@7f231fc9([Name(non spatial determintic), key(308949947), Owner(Sybren(304037797)), GroupAccess(Private), BranchPointRef(null), BranchID(308044382), Flag(Current), Date(02-Apr-2026 08:01:57), 
......
java.lang.NullPointerException: Cannot invoke \"cbit.vcell.mapping.stoch.MassActionStochasticFunction.forwardRate()\" because \"maFunc\" is null\r
	at cbit.vcell.mapping.ParticleMathMapping.refreshMathDescription(ParticleMathMapping.java:732)\r
	at cbit.vcell.mapping.ParticleMathMapping.refresh(ParticleMathMapping.java:1073)\r
	at cbit.vcell.mapping.AbstractMathMapping.getMathDescription(AbstractMathMapping.java:888)\r
	at cbit.vcell.mapping.AbstractMathMapping.getMathDescription(AbstractMathMapping.java:902)\r
	at cbit.vcell.client.task.DocumentValidTask.run(DocumentValidTask.java:68)\r
	at cbit.vcell.client.task.ClientTaskDispatcher.runTask(ClientTaskDispatcher.java:677)\r
	at cbit.vcell.client.task.ClientTaskDispatcher$1.construct(ClientTaskDispatcher.java:380)\r
	at swingthreads.SwingWorker$2.run(SwingWorker.java:109)\r
	at java.base/java.lang.Thread.run(Thread.java:833)\r
","softwareVersion":"Rel_Version_7.7.0_build_47","platform":"Running under Java 17.0.7, published by JetBrains s.r.o., on the amd64 architecture running version 10.0 of the Windows 11 operating system"}

The model may be entirely corrupted, the stack trace is full of all sort of exceptions