In fact, the Code of Hammurabi has law #12 followed by law #14.
You are refering to the English transcription by L.W. King
from 1915, I suppose? He accidentially left out law #12, gave the actual #13 erroneousely the number 12 and then continued correctly with 14.
There is a correct and complete translation by Gressmann
from 1926 available in German.
The law King left out is: (please pardon my somewhat free phrasing - I am unfamiliar with English legal terms)
#12: if the seller has died meanwhile, the purchaser is allowed to take from his house a sum 5 times worth the sum of what the legal fight is about.
Then follows #13 (wrongly numbered 12 by King): If the witnesses be not at hand, then shall the judge set a limit at the expiration of 6 months. ... etc.etc.
After that comes #14 (correctly numbered again): if anyone steal the minor son of another, he shall be put to death.
(Here King makes a slight mistake: it's actually: if anyone steals a freeborn
minor (freeborn as opposed to a slave which case will be dealt woth in rule #15)