How to test if some command similar to \author is used in .tex file?

Question

I want to modify \maketitle command in a new document class based in memoir. \maketitle command should include a new \director command similar to author. If this command is defined in text file, the word Director (or Directors) followed by director's name is included in title but if not defined, nothing should appear.

Next code is a combination of the answers in How to count the number of authors of a document? and How to make a new command similar to \author. With second answer project directors name is added to title with \maketitle command and with the first one, the word Director or Directors is selected according command \and appering in \director command.

The problem is how to test if command \director is not used in order to avoid 'Director'. I know how to add a \newif\director but not where to set and use.

\documentclass{memoir}% http://ctan.org/pkg/memoir
\makeatletter
\newcommand{\director}[1]{\gdef\@director{#1}}%
\newcommand{\@director}{\@latex@warning@no@line{No \noexpand\director given}}
\addtoiargdef{\director}{%
  \begingroup\let\footnote\@gobble}{%
  \begingroup
    \renewcommand{\thanks}[1]{}
    \renewcommand{\and}{\unskip, }
    \renewcommand{\andnext}{\unskip, }
    \renewcommand{\thanksmark}[1]{}
    \renewcommand{\thanksgap}[1]{}
    \protected@xdef\thedirector{#1}
  \endgroup\endgroup}
\newcommand{\predirector}[1]{\def\@bspredirector{#1}}
\newcommand{\postdirector}[1]{\def\@bspostdirector{#1}}
\renewcommand{\maketitlehookc}{%
  {\@bspredirector \@director \@bspostdirector}%
}
\predirector{\begin{center}
  \large \lineskip .5em%
    \printdirector\par
  \begin{tabular}[t]{c}}
\postdirector{\end{tabular}\par\end{center}}

\newcommand\testdirector{%
        \expandafter\tst@dir\@director\and\nil%
}
\def\tst@dir#1\and#2\nil{%
        \edef\test{#2}%
        \ifx\test\@empty Director\else Directors\fi%
}
\newcommand\printdirector{%
        {%
        \protected\def\and{and }%
        \large \testdirector\par}
        }
\makeatother

\title{A Title}
\author{An Author \and Another Author}
%\director{My Director \and My other Director}
%\director{My Director}
\date{\today}
\begin{document}

\maketitle

\end{document}

Answer 1

Since \director seems to be optional, say

\let\@director\@empty

instead of

\newcommand{\@director}{\@latex@warning@no@line{No \noexpand\director given}}

Then try

\renewcommand{\maketitlehookc}{%
  \ifx\@director\@empty
  \else{\@bspredirector \@director \@bspostdirector}%
  \fi}

So, if a \director command has not been issued, the test will be true and the \else part will be skipped.

Answer 2

If \director is optional then you don't want

 \newcommand{\@director}{\@latex@warning@no@line{No \noexpand\director given}}

you just want

 \newcommand{\@director}{}

Then (more or less) you don't need to test anything, just use \@director and it will be the author supplied name or nothing. You may need to make it a bit more complicated depending what you want to do pre and post director in the default (empty) case. I wasn't clear on that. But you could for example make all three internal commands empty and make director define the pre and post commands to use some spacing. So again, no testing is needed.