Not only does this leave open a risk to crash the node for the check in `_compressible()` but also is the `tmp` check below getting confused when `ptr` is `NULL`, since `gnrc_pktbuf_start_write()` returns `NULL` in that case.
Not only does this leave open a risk to crash the node for the check in `_compressible()` but also is the `tmp` check below getting confused when `ptr` is `NULL`, since `gnrc_pktbuf_start_write()` returns `NULL` in that case.