[FFmpeg-user] Unable to parse option value "(null)" as sample format

[Madovsky]

last git installed.
with this command line

ffmpeg -i test.wav -vn -acodec libfdk_aac -y test.mp4

I got

ffmpeg version N-71839-g6197672 Copyright (c) 2000-2015 the FFmpeg 
developers
   built with gcc 4.9.2 (GCC) 20150212 (Red Hat 4.9.2-6)
   configuration: --enable-static --enable-gpl --enable-nonfree 
--enable-libfaac --enable-libx264 --enable-libspeex --enable-librtmp 
--enable-runtime-cpudetect --enable-libfreetype --enable-iconv 
--enable-x11grab --enable-libfdk_aac --enable-libopenh264 --disable-asm 
--enable-pthreads --enable-libx265
   libavutil      54. 23.101 / 54. 23.101
   libavcodec     56. 35.101 / 56. 35.101
   libavformat    56. 31.100 / 56. 31.100
   libavdevice    56.  4.100 / 56.  4.100
   libavfilter     5. 14.100 /  5. 14.100
   libswscale      3.  1.101 /  3.  1.101
   libswresample   1.  1.100 /  1.  1.100
   libpostproc    53.  3.100 / 53.  3.100
[wav @ 0x30ac000] Could not find codec parameters for stream 0 (Audio: 
pcm_s16le ([1][0][0][0] / 0x0001), 8000 Hz, 1 channels, 128 kb/s): 
unspecified sample format
Consider increasing the value for the 'analyzeduration' and 'probesize' 
options
test.wav: could not find codec parameters
Guessed Channel Layout for  Input Stream #0.0 : mono
Input #0, wav, from 'test.wav':
   Duration: N/A, bitrate: 128 kb/s
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 8000 Hz, 1 
channels, 128 kb/s
[abuffer @ 0x3072250] Unable to parse option value "(null)" as sample format
     Last message repeated 1 times
[abuffer @ 0x3072250] Error setting option sample_fmt to value (null).
[graph 0 input from stream 0:0 @ 0x30abd20] Error applying options to 
the filter.
Error opening filters!



was working before for 2 years since the last git update

thanks

Franck