RFC6592

Many experts naively confuse the Null Packet with an Imaginary Packet, in a rationalization attempt when faced with the inability to prove the existence of the Null Packet. For reference, an Imaginary Packet contains the IP Version of 4i or 6i. However, protocol purists are not fooled and quickly plea with experts to get real. The Null Packet's qualities should not be confused with the bit-bucket blackhole nature of the null device, since the Null Packet does not discard packets. Confusion might stem from the fact that the behavior is similar to that of input streams reading from /dev/ null (i.e., "nothing is returned").

The Null Packet - rfc6592