Beamer template problem: flushright frame subtitle causes spurious extra slide (or worse!)

Question

So here is a MWE that illustrates the problem.

\documentclass{beamer}
\defbeamertemplate{frametitle}{weird}{%
  \insertframetitle\par%
  \rule{\textwidth}{4pt}%
  \flushright%
  \insertframesubtitle\par%
}
\setbeamertemplate{frametitle}[weird]
\begin{document}
\begin{frame}
\frametitle{Here is the title}
%\framesubtitle{Here is the subtitle}
Here is the text
\pause
Here is more text
\end{frame}
\end{document}

This code fails with a:

! LaTeX Error: Something's wrong--perhaps a missing \item.

Commenting out the \pause or \flushright or uncommenting the \framesubtitle allows it to compile. [Commenting out the \pause leads to a spurious empty page at the end.]

So my guess is that this is a "wrong mode" problem when the subtitle is empty. But I don't know enough to fix it. Any clues? Or any hints on what to try in order to fix it?

Answer 1

where is the sense to use the two macros instead of using the arguments of frame? This works:

\begin{frame}{Here is the title}{Here is the subtitle}


you should also check for an existing subtitle:

\documentclass{beamer}
\makeatletter
\defbeamertemplate{frametitle}{weird}{%
  \insertframetitle\par%
  \rule{\textwidth}{4pt}%
  \ifx\insertframesubtitle\@empty\else
  \flushright%
  \insertframesubtitle\par\fi}
\makeatother
\setbeamertemplate{frametitle}[weird]
\begin{document}
\begin{frame}{Here is the title}{}
Here is the text
\pause
Here is more text
\end{frame}
\end{document}