Use nullrev+count instead of count-1 in a newly introduced expression.
Before that repo.changelog.tip() was used, but this yields a node.
Of course many more places should be changed like this, this was just done
as an example.
#header#
<title>Mercurial Error</title>
</head>
<body>
<h2>Mercurial Error</h2>
<p>
An error occured while processing your request:
</p>
<p>
#error|escape#
</p>
#footer#