Strange code in `nnimap-open-connection-1'

[Deniz Dogan]

In `nnimap-open-connection-1' I read:

[...]
    (let* ((coding-system-for-read 'binary)
           (coding-system-for-write 'binary)
           (port nil)
[...]

`port' is set to nil but the value is never used except for in the error 
message: (nnheader-report 'nnimap "Unable to contact %s:%s via %s" 
nnimap-address port nnimap-stream)

This is confusing to say the least.  What is going on here?

Deniz