libavcodec/aac.c:1557: error: Null Dereference
  pointer `&gb->buffer` last assigned on line 1555 could be null and is dereferenced by call to `show_bits()` at line 1557, column 9.

libavcodec/aac.c:1549:1: start of procedure aac_decode_frame()
1547. }
1548. 
1549. static int aac_decode_frame(AVCodecContext * avccontext, void * data, int * data_size, const uint8_t * buf, int buf_size) {
      ^
1550.     AACContext * ac = avccontext->priv_data;
1551.     GetBitContext gb;

libavcodec/aac.c:1550:5: 
1548. 
1549. static int aac_decode_frame(AVCodecContext * avccontext, void * data, int * data_size, const uint8_t * buf, int buf_size) {
1550.     AACContext * ac = avccontext->priv_data;
          ^
1551.     GetBitContext gb;
1552.     enum RawDataBlockType elem_type;

libavcodec/aac.c:1555:5: 
1553.     int err, elem_id, data_size_tmp;
1554. 
1555.     init_get_bits(&gb, buf, buf_size*8);
          ^
1556. 
1557.     if (show_bits(&gb, 12) == 0xfff) {

libavcodec/bitstream.h:737:1: start of procedure init_get_bits()
  735.  * @param bit_size the size of the buffer in bits
  736.  */
  737. static inline void init_get_bits(GetBitContext *s,
       ^
  738.                    const uint8_t *buffer, int bit_size)
  739. {

libavcodec/bitstream.h:740:5: 
  738.                    const uint8_t *buffer, int bit_size)
  739. {
  740.     int buffer_size= (bit_size+7)>>3;
           ^
  741.     if(buffer_size < 0 || bit_size < 0) {
  742.         buffer_size = bit_size = 0;

libavcodec/bitstream.h:741:8: Taking true branch
  739. {
  740.     int buffer_size= (bit_size+7)>>3;
  741.     if(buffer_size < 0 || bit_size < 0) {
              ^
  742.         buffer_size = bit_size = 0;
  743.         buffer = NULL;

libavcodec/bitstream.h:742:9: 
  740.     int buffer_size= (bit_size+7)>>3;
  741.     if(buffer_size < 0 || bit_size < 0) {
  742.         buffer_size = bit_size = 0;
               ^
  743.         buffer = NULL;
  744.     }

libavcodec/bitstream.h:743:9: 
  741.     if(buffer_size < 0 || bit_size < 0) {
  742.         buffer_size = bit_size = 0;
  743.         buffer = NULL;
               ^
  744.     }
  745. 

libavcodec/bitstream.h:746:5: 
  744.     }
  745. 
  746.     s->buffer= buffer;
           ^
  747.     s->size_in_bits= bit_size;
  748.     s->buffer_end= buffer + buffer_size;

libavcodec/bitstream.h:747:5: 
  745. 
  746.     s->buffer= buffer;
  747.     s->size_in_bits= bit_size;
           ^
  748.     s->buffer_end= buffer + buffer_size;
  749. #ifdef ALT_BITSTREAM_READER

libavcodec/bitstream.h:748:5: 
  746.     s->buffer= buffer;
  747.     s->size_in_bits= bit_size;
  748.     s->buffer_end= buffer + buffer_size;
           ^
  749. #ifdef ALT_BITSTREAM_READER
  750.     s->index=0;

libavcodec/bitstream.h:750:5: 
  748.     s->buffer_end= buffer + buffer_size;
  749. #ifdef ALT_BITSTREAM_READER
  750.     s->index=0;
           ^
  751. #elif defined LIBMPEG2_BITSTREAM_READER
  752.     s->buffer_ptr = (uint8_t*)((intptr_t)buffer&(~1));

libavcodec/bitstream.h:760:1: return from a call to init_get_bits
  758.     skip_bits_long(s, 0);
  759. #endif
  760. }
       ^
  761. 
  762. static inline void align_get_bits(GetBitContext *s)

libavcodec/aac.c:1557:9: 
1555.     init_get_bits(&gb, buf, buf_size*8);
1556. 
1557.     if (show_bits(&gb, 12) == 0xfff) {
              ^
1558.         if ((err = parse_adts_frame_header(ac, &gb)) < 0) {
1559.             av_log(avccontext, AV_LOG_ERROR, "Error decoding AAC frame header.\n");

libavcodec/bitstream.h:648:1: start of procedure show_bits()
  646.  * Note, the alt bitstream reader can read up to 25 bits, but the libmpeg2 reader can't
  647.  */
  648. static inline unsigned int show_bits(GetBitContext *s, int n){
       ^
  649.     register int tmp;
  650.     OPEN_READER(re, s)

libavcodec/bitstream.h:650:5: 
  648. static inline unsigned int show_bits(GetBitContext *s, int n){
  649.     register int tmp;
  650.     OPEN_READER(re, s)
           ^
  651.     UPDATE_CACHE(re, s)
  652.     tmp= SHOW_UBITS(re, s, n);

libavcodec/bitstream.h:651:5: 
  649.     register int tmp;
  650.     OPEN_READER(re, s)
  651.     UPDATE_CACHE(re, s)
           ^
  652.     tmp= SHOW_UBITS(re, s, n);
  653. //    CLOSE_READER(re, s)
