array and matrix environments don't ignore trailing newlines

[wchargin]

Everyone likes trailing commas! But trailing newlines in matrices seem to add an extra newline 😢

LaTeX source to test:

\documentclass{article}

\pagestyle{empty}

\usepackage{amsmath}

\begin{document}

\[
  \begin{bmatrix}
    a & b \\
    c & d \\ 
  \end{bmatrix}
\]

\end{document}

LaTeX output:

KaTeX output:

[wchargin]

For reference, the Other Library has the behavior of LaTeX:

[xymostech]

👍 Thanks for this! Trailing newlines should definitely be accepted.