beamer + biblatex: authoryear causes problem with "insertbiblabel"

With biblatex, insertbiblabel only works with styles that have a labelled bibliography list (numeric and alphabetic styles; to see what it means to have a 'labelled' bibliography list compare the output of style=alphabetic, and style=authoryear, with documentclass{article}). The authoryear style does not have a labelled bibliography list and it does not repeat the citation labels in the bibliography.

So with authoryear there simply is no label for insertbiblabel to insert.

I would just use

documentclass{beamer}

usepackage[style=authoryear]{biblatex}

addbibresource{biblatex-examples.bib}

setbeamertemplate{bibliography item}{}

begin{document}
begin{frame}
  cite{doody,sigfridsson}
end{frame}

begin{frame}[allowframebreaks]
  frametitle{References}
  printbibliography
end{frame}
end{document}

which gives you fundamentally the same output as with documentclass{article}.

---

If you want to repeat the citation labels in the bibliography to make it easier to find entries, you can use biblatex-ext as follows

documentclass{beamer}

usepackage[backend=biber,
  bibstyle=ext-authoryear,
  citestyle=ext-authoryear,
  sorting=nyt,
  introcite=label,
]{biblatex}

addbibresource{biblatex-examples.bib}

setbeamertemplate{bibliography item}{insertbiblabel}

% avoid error about insertbiblabel being undefined
preto{bibsetup}{providecommand*{insertbiblabel}{}}

begin{document}
begin{frame}
  cite{doody,sigfridsson}
end{frame}

begin{frame}[allowframebreaks]
  frametitle{References}
  printbibliography
end{frame}
end{document}