[HACKERS] incompatible changes of PQsetdbLogin()

[Tatsuo Ishii]

It seems some incompatible changes have been made between 7.0 and
current. In 7.0, if a parameter is NULL OR a null string (""), then
the value from an environment variable is applied. However in current
ONLY NULL is considered. Is there any reason for this?
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Tatsuo Ishii