pgfplots: nan in meta expr causes “Missing number” error

I want to draw a table/matrix of color-values, where some of the values are missing. Despite having tried using unbounded coords=jump (see this answer), I get the following error:

! Missing number, treated as zero.
n
l.59 \end{axis}

How do I tell pgfplots to include the rows and columns for the missing value, and simply skip those missing value?

Here's my MWE:

\documentclass{standalone}

\usepackage{filecontents}
\usepackage{pgfplots, pgfplotstable}

\begin{filecontents}{data.csv}
yitem,xitem,val
a,R,0.1
b,S,nan
c,T,0.3
d,U,nan
e,V,0.5
f,W,0.6
g,X,nan
h,Y,0.8
i,Z,nan
\end{filecontents}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
symbolic x coords={R,S,T,U,V,W,X,Y,Z},
xtick=data,
symbolic y coords={a,b,c,d,e,f,g,h,i},
ytick=data,
unbounded coords=jump,
]
mark=square*,
only marks,
scatter,
point meta=explicit,
] table [
col sep=comma,
x expr=\coordindex,
y expr=\coordindex,
meta expr=\thisrow{val},
] {\datatable};

\end{axis}
\end{tikzpicture}
\end{document}


I have added \listfiles to my preamble and received the following pgf-looking output:

pgfplots.sty    2011/12/29 v1.5.1 (git show 1.5.1-4-g53e640f )
pgf.sty    2008/01/15 v2.10 (rcs-revision 1.12)
pgfrcs.sty    2010/10/25 v2.10 (rcs-revision 1.24)
pgfrcs.code.tex
pgfcore.sty    2010/04/11 v2.10 (rcs-revision 1.7)
pdftex.def    2011/05/27 v0.06d Graphics/color for pdfTeX
pgfsys.sty    2010/06/30 v2.10 (rcs-revision 1.37)
pgfsys.code.tex
pgfsyssoftpath.code.tex    2008/07/18  (rcs-revision 1.7)
pgfsysprotocol.code.tex    2006/10/16  (rcs-revision 1.4)
pgfcore.code.tex
pgfcomp-version-0-65.sty    2007/07/03 v2.10 (rcs-revision 1.7)
pgfcomp-version-1-18.sty    2007/07/23 v2.10 (rcs-revision 1.1)
pgffor.sty    2010/03/23 v2.10 (rcs-revision 1.18)
pgfkeys.sty
pgfkeys.code.tex
pgffor.code.tex
pgfplotstable.sty    2011/12/19 Part of pgfplots
• I don't get an error when running this code. What version of PGFPlots are you using? – Jake Jan 13 '14 at 15:12
• I added some output. It looks like its version 1.5.1 – derabbink Jan 13 '14 at 15:24
• The current version is 1.9. Could you update the package and check whether the error persists? – Jake Jan 13 '14 at 15:24
• I updated to 1.9 as you suggested, and now it works. If you want to type that up as an answer, I'll make sure to accept it. – derabbink Jan 14 '14 at 8:56