BIO_f_null — null filter
BIO_f_null() returns the null filter BIO method. This is a
filter BIO that does nothing.
All requests to a null filter BIO are passed through to the
next BIO in the chain: this means that a BIO chain containing a
null filter BIO behaves just as though the BIO was not there.
As may be apparent a null filter BIO is not particularly useful.
BIO_f_null() returns the null filter BIO method.