Crash when Boogie receives SIGINT

[keyboardDrummer]

When verifying a closed-source Dafny program and pressing ctrl+C in the shell, the following exception occurs.

Unhandled exception. System.AggregateException: One or more errors occurred. (Object reference not set to an instance of an object.)
 ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Boogie.SMTLib.SMTLibProcess.Send(String cmd)
   at Microsoft.Boogie.SMTLib.SMTLibProcess.PingPong()
   at Microsoft.Boogie.Checker.GoBackToIdle()
   at VC.SplitAndVerifyWorker.DoWork(Int32 iteration, Split split, CancellationToken cancellationToken)
   at VC.SplitAndVerifyWorker.DoWorkForMultipleIterations(Split split, CancellationToken cancellationToken)
   at VC.SplitAndVerifyWorker.WorkUntilDone(CancellationToken cancellationToken)
   at VC.VCGen.VerifyImplementation(ImplementationRun run, VerifierCallback callback, CancellationToken cancellationToken)
   at VC.ConditionGeneration.VerifyImplementation(ImplementationRun run, CancellationToken cancellationToken)
   at Microsoft.Boogie.ExecutionEngine.VerifyImplementationWithoutCaching(ProcessedProgram processedProgram, PipelineStatistics stats, ErrorReporterDelegate er, CancellationToken cancellationToken, String programId, Implementation impl, TextWriter traceWriter)
   at Microsoft.Boogie.ExecutionEngine.VerifyImplementation(ProcessedProgram processedProgram, PipelineStatistics stats, ErrorReporterDelegate er, CancellationToken cancellationToken, Implementation implementation, String programId, TextWriter traceWriter)
   at Microsoft.Boogie.ExecutionEngine.<>c__DisplayClass38_0.<<VerifyEachImplementation>b__1>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.Boogie.ExecutionEngine.<>c__DisplayClass38_0.<<VerifyEachImplementation>b__1>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.Boogie.ExecutionEngine.VerifyEachImplementation(TextWriter output, ProcessedProgram processedProgram, PipelineStatistics stats, String programId, ErrorReporterDelegate er, String requestId, Implementation[] stablePrioritizedImpls)
   at Microsoft.Boogie.ExecutionEngine.InferAndVerify(TextWriter output, Program program, PipelineStatistics stats, String programId, ErrorReporterDelegate er, String requestId)
   at Microsoft.Dafny.Main.BoogiePipelineWithRerun(TextWriter output, ExecutionEngine engine, Program program, String bplFileName, String programId)
   at Microsoft.Dafny.Main.BoogieOnce(TextWriter output, ExecutionEngine engine, String baseFile, String moduleName, Program boogieProgram, String programId)
   at Microsoft.Dafny.DafnyDriver.BoogieOnceWithTimerAsync(TextWriter output, String baseName, String programId, String moduleName, Program program)
   at Microsoft.Dafny.DafnyDriver.<>c__DisplayClass20_0.<<BoogieAsync>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.Dafny.DafnyDriver.<>c__DisplayClass20_0.<<BoogieAsync>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.Dafny.DafnyDriver.BoogieAsync(String baseName, IEnumerable`1 boogiePrograms, String programId)
   at Microsoft.Dafny.DafnyDriver.ProcessFilesAsync(IList`1 dafnyFiles, ReadOnlyCollection`1 otherFileNames, ErrorReporter reporter, Boolean lookForSnapshots, String programId)
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at System.Threading.Tasks.Task`1.get_Result()
   at Microsoft.Dafny.DafnyDriver.ThreadMain(String[] args)
   at Microsoft.Dafny.DafnyDriver.<>c__DisplayClass10_0.<Main>b__0()
   at System.Threading.Thread.StartCallback()