This particular change was part of the sysctl net: Remove unused binary sysctl code commit by Eric W. Biederman, changing the initialization of the last element of the ip_ct_sysctl_table array from {0} to {} (and performs similar changes to many other array initializations).
The {0} pattern seems to have been around for much longer though, and both {0} or {} final element-initialization is commonly (in the Linux source code) explicitly referred to as Terminating entry, so it is likely a pattern present to allow consuming these arrays without knowing their lengths, terminating consumption when hitting the zero-initialized terminating entry. E.g. for the similar arrays in sound/aoa/fabrics/snd-aoa-fabric-layout.c the intent of the zero-initialization is even explicitly mentioned in a comment, e.g.:
static struct codec_connection toonie_connections[] = { { .connected = CC_SPEAKERS | CC_HEADPHONE, .codec_bit = 0, }, {} /* terminate array by .connected == 0 */ };