In biblatex.def, the bibmacro name:first-last is defined as
\newbibmacro*{name:first-last}[4]{%
...
\ifprefchar{}
{}
{\ifuseprefix{\bibnamedelimc}{\bibnamedelimd}}}%
...
But \ifprefchar takes two arguments, not three.
I think the definition should be
\newbibmacro*{name:first-last}[4]{%
...
\ifprefchar
{}
{\ifuseprefix{\bibnamedelimc}{\bibnamedelimd}}}%
...
In some cases, this inserts an extra space between the first and the last names.