Spurious blank row with longtable and expl3 map function

I’ve got some data in an expl3 sequence, which I’m using in a longtable. All works fine, but I’m getting an additional blank row after the inline map body. MWE:

documentclass{article}
usepackage{expl3}
usepackage{xparse}
usepackage{longtable}

ExplSyntaxOn

NewDocumentCommand{printData}{}
 {
   begin{longtable}{l}
     hline
     Minimal~Working~Example 
     hline
     endhead
     End 
     hline
     endfoot
     clist_map_inline:nn
       {comma,separated,list,of,data,also,fails,with,seq}
       {
         ##1 
         hline
       }
% Uncomment to fill the blank row
%       Mystery row here!  hline
   end{longtable}
 }

ExplSyntaxOff

begin{document}
printData
end{document}

Which produces:

The intention is for the final loop of the inline map to close with an hline, running straight into the footer. I’m on an older version of texlive and pdflatex (from Ubuntu 18.04), but this error is also present on overleaf, which I’m assuming is up to date, so I presume the error is mine.

documentclass{article}
usepackage{expl3}
usepackage{xparse}
usepackage{longtable}

ExplSyntaxOn

NewDocumentCommand{printData}{}
 {
  begin{longtable}{l}
  hline
  Minimal~Working~Example 
  hline
  endhead
  End 
  hline
  endfoot
  clist_map_function:nN {comma,separated,list,of,data} aejh_entry:n
  end{longtable}
 }

cs_new_protected:Nn aejh_entry:n { #1  hline }

ExplSyntaxOff

begin{document}

printData

end{document}