why does hall of fame return nan ocassionally?

[Akhilnandh]

Hi, I find that when I am running an optimisation algorithm using evolutionary strategies, the hall of fame returns 'nan' values ocassionally, for no particular reason. I usually invalidate unfit individuals by assigning a very large number- 1e38, but I found it strange that HoF does not recognise any number, but returns 'nan'

Any help regarding this will be useful