[Tex/LaTex] Problem using \alert{} in Beamer title with metropolis theme

beamercolorformattingthemestitles

I'm trying to emphasize some words in the title of a beamer document. Ex :

\documentclass{beamer}
  \usepackage[utf8]{inputenc}
  \usetheme{Warsaw}%\usetheme{m}%-->problem

    \usepackage{tikz}
    \usetikzlibrary{arrows,shapes}


  \title{Hello \protect\alert{World}!}
  \author{}

  \begin{document}

  \begin{frame}
  \titlepage
  \end{frame}

  \end{document}

Which gives the following result :

But I want to use a theme for the document ( metropolis : see https://github.com/matze/mtheme ). The problem is that errors appear during compilation while using this theme instead of Warsaw theme. The error message is :

"! Undefined control sequence.
\beamer@sort #1#2->\long \def \beamer@todo
{#1}\def \beamer@ospec {}\beamer@...
l.12 \end{frame}
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.
! Argument of \beamerx@\alert has an extra }.
<inserted text>
..."

Is there a way to emphasize some part of the title using this theme (with \alert{} or \textbf or other environment) ?

Best Answer

If \title is defined after \begin{document} but before \maketitle, the problem is solved.

\documentclass{beamer}
\usepackage[utf8]{inputenc}
\usetheme{m}%\usetheme{m}%-->problem

\usepackage{tikz}
\usetikzlibrary{arrows,shapes}


\begin{document}
\author{}
\title{Hello \protect\alert{World}!}

\begin{frame}
\titlepage
\end{frame}

\end{document}

Similar solution can be applied with other themes when TiKZ is used.