PVS-Studio warning V595 for OpenSSL

int OBJ_obj2txt(char *buf, int buf_len,
  const ASN1_OBJECT *a, int no_name)
{
  ....
  if ((a == NULL) || (a->data == NULL)) {
    buf[0]='\0';
    return(0);
  }
  ....
  if (buf)
  ....
}

This suspicious code was found in OpenSSL project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'buf' pointer was utilized before it was verified against nullptr. Check lines: 448, 461. obj_dat.c 448

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