The Collaborative International Dictionary of English v.0.48:

Nul \Nul\, a. [F. See Null, a.] (Law)
   No; not any; as, nul disseizin; nul tort.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

NUL, law French. A barbarous word which means to convey a negative; as, Nul
tiel record, Nul tiel award.