Hi,

including font-otp triggers an error with the Amiri font:

    ! LuaTeX error ./luaotfload-merged.lua:10471: invalid value
    (nil) at index 1 in table for 'concat'.

Which corresponds to line 192 of font-otp.lua. Test code:

    \font\test={file:amiri-regular.ttf}
    \test ضرب
    \bye

Or with Context:

    \mainlanguage[arabic]
    \definefontsynonym[amiri][file:amiri-regular.ttf]

    \starttext
      \definedfont[amiri*arabic at 42pt]
      \setupalign[r2l]
      ضرب 0123456789
    \stoptext

I have tested the Amiri files from TeX Live 2012 and 2013. Can
somebody reproduce this, possibly with other fonts? Scheherazade
works fine.

Thanks for any advice
Philipp