Variabel Einträge (Zahl/Buchstaben) im Eintragsfeld number = {}

\begin{filecontents}{\jobname.bib}
@Article{Test2012,
  author    = {Test, Tester},
  title     = {Testing the Tests},
  journal   = {Journal of testing Test},
  year      = {2012},
  volume    = {11},
  pages     = {5--39},
  number    = {1},
   publisher = {Testing Publishing},
}
@Article{Test2014,
  Title                    = {Test ohne Zeitschriftennummer},
  Author                   = {Super Supertest},
  journal   = {Journal of testing Test},
  Volume                   = {32},
  Year                     = {2014},
    pages     = {40--50},
  Number                   = {k. A.},
   publisher = {Testing Publishing},
}
\end{filecontents}
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\begin{document}
\cite[][]{Test2012} und \cite[][]{Test2014} 
\printbibliography
\end{document}