Handle unset notBefore and notAfter values
diff --git a/doc/pyOpenSSL.tex b/doc/pyOpenSSL.tex
index ec8831d..5e4d531 100644
--- a/doc/pyOpenSSL.tex
+++ b/doc/pyOpenSSL.tex
@@ -297,6 +297,7 @@
YYYYMMDDhhmmss+hhmm
YYYYMMDDhhmmss-hhmm
\end{verbatim}
+If no value exists for this field, \code{None} is returned.
\end{methoddesc}
\begin{methoddesc}[X509]{get_notAfter}{}
@@ -307,6 +308,7 @@
YYYYMMDDhhmmss+hhmm
YYYYMMDDhhmmss-hhmm
\end{verbatim}
+If no value exists for this field, \code{None} is returned.
\end{methoddesc}
\begin{methoddesc}[X509]{set_notBefore}{when}