sraSpanInsertAfter(sraSpan *newspan, sraSpan *after) {
  if(newspan && after) {
    newspan->_next = after->_next;
    newspan->_prev = after;
    after->_next->_prev = newspan;
    after->_next = newspan;
  }
}
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.