Empty theorem environments with "theorem name" do not render properly

[leorolla]

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\documentclass[11pt]{amsart}
\title{Bug report}
\usepackage{bookml/bookml}
\begin{document}
\newtheorem{exercisenonumber}{}
\newtheorem{theorem}{Theorem}
\begin{exercisenonumber}
[Exercise name]
Test
\end{exercisenonumber}
\begin{theorem}
[Theorem name]
Test
\end{theorem}
\end{document}