Auf sowas kannst du mit `\iffieldundef{fieldname}{dann}{sonst}` testen.
Beispielsweise:
\iffieldundef{version}{%
{\color{red} sorry, no version available}%
}{%
\printfield{version}%
}%
Im ganzen sähe das ganze dann etwa so aus, allerdings würde ich da noch ein paar Schönheitskorrekturen machen ;-)
![dzaicIffieldundef][1]
% Filecontents; handle with care!
\begin{filecontents}{\jobname.bbx}
\ProvidesFile{\jobname.bbx}[2012/02/20 v1.0 biblatex
bibliography style]
\ProvidesFile{\jobname.bbx}[2014/12/16 v0.1 TeXwelt test]
\RequireBibliographyStyle{numeric}
\DeclareNameAlias{mydate}{default}
\DefineBibliographyStrings{english}{version={Rev.}}
\renewcommand*{\newunitpunct}{\addsemicolon\addspace}
\DeclareFieldFormat[report]{title}{\mkbibquote{#1}}
\DeclareBibliographyDriver{report}{%
\printlist{institution}%
\newunit%
\printnames{author}%
\newunit%
\printfield{title}%
\newunit
\printfield{number}%
\newunit%
\iffieldundef{version}{%
{\color{red} sorry, no version available}%
}{%
\printfield{version}%
}%
\newunit%
\iffieldundef{day}{}{%
\printfield{day}.\addspace}%
\printfield{month}
\printfield{year}%
\finentry%
}
\endinput
\end{filecontents}
\begin{filecontents}{\jobname.bib}
@REPORT{APOSTO,
author = {G. Apostolakis},
title = {Data specialization for plant specific risk studies},
institution = {Nuclear Engineering and Design 56},
number = {321-329},
date = {1979-07-12}
}
@REPORT{RiskSpectrumTheoryManual,
author = {Relcon Scandpower AB},
title = {RiskSpectrum Analysis Tools - Theory Manual},
number = {BET/07/0286},
version = {3.2.1},
date = {2012-08}
}
\end{filecontents}
\documentclass{scrartcl}
\usepackage[bibstyle=\jobname,backend=biber]{biblatex}
\addbibresource{\jobname.bib}
\usepackage{xcolor}
\begin{document}
no version: \cite{APOSTO}\par
no day: \cite{RiskSpectrumTheoryManual}\par
\printbibliography
\end{document}
[1]: http://texwelt.de/wissen/upfiles/dzaicIffieldundef.png
