libavcodec/imgconvert.c:56: error: Null Dereference
  pointer `desc` last assigned on line 55 could be null and is dereferenced at line 56, column 16.

libavcodec/imgconvert.c:53:1: start of procedure avcodec_get_chroma_sub_sample()
51. #endif
52. 
53. void avcodec_get_chroma_sub_sample(enum AVPixelFormat pix_fmt, int *h_shift, int *v_shift)
    ^
54. {
55.     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(pix_fmt);

libavcodec/imgconvert.c:55:5: 
53. void avcodec_get_chroma_sub_sample(enum AVPixelFormat pix_fmt, int *h_shift, int *v_shift)
54. {
55.     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(pix_fmt);
        ^
56.     *h_shift = desc->log2_chroma_w;
57.     *v_shift = desc->log2_chroma_h;

libavutil/pixdesc.c:1434:1: start of procedure av_pix_fmt_desc_get()
  1432. }
  1433. 
  1434. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
        ^
  1435. {
  1436.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)

libavutil/pixdesc.c:1436:9: Taking false branch
  1434. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1435. {
  1436.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                ^
  1437.         return NULL;
  1438.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1436:24: Taking true branch
  1434. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1435. {
  1436.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                               ^
  1437.         return NULL;
  1438.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1437:9: 
  1435. {
  1436.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
  1437.         return NULL;
                ^
  1438.     return &av_pix_fmt_descriptors[pix_fmt];
  1439. }

libavutil/pixdesc.c:1439:1: return from a call to av_pix_fmt_desc_get
  1437.         return NULL;
  1438.     return &av_pix_fmt_descriptors[pix_fmt];
  1439. }
        ^
  1440. 
  1441. const AVPixFmtDescriptor *av_pix_fmt_desc_next(const AVPixFmtDescriptor *prev)

libavcodec/imgconvert.c:56:5: 
54. {
55.     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(pix_fmt);
56.     *h_shift = desc->log2_chroma_w;
        ^
57.     *v_shift = desc->log2_chroma_h;
58. }
