This is an annoying bug, and very hard to pin down (took me half a day to figure out that it was caused by execution in scheduled space) when encountered by developers because it occurs in valid code.
It is working CORRECTLY in non-scheduled execution! This is the incorrect method of raising this error! Assigning nil to a variable is incredibly important for any complex SQF functionality, especially in dynamic function calling where the return value may be different all the time and returning nil from an inner function is desired.