jdk.vm.ci.hotspot.HotSpotStackIntrospection#iterateFrames uses jdk.vm.ci.hotspot.CompilerToVM#getNextStackFrame to iterate frames. The first argument is a "reference" frame from which the stack-walk starts.

During the first call to getNextStackFrame null is passed and for subsequent calls the previous value returned from getNextStackFrame is passed.
This can be a problem if iterateFrames itself (or in general the compilation unit containing iterateFrames) uncommon traps: if the "current" frame refers to that compilation unit during the uncommon trap, the next call to getNextStackFrame will throw IllegalStateException: stack frame not found because the frame search is based on the stack point and the uncommon trap might change that.