Section 3--115. Incomplete Instruments.

(1) When a paper whose contents at the time of signing show that it is
intended to become an instrument is signed while still incomplete in any
necessary respect it cannot be enforced until completed, but when it is
completed in accordance with authority given it is effective as
completed.

(2) If the completion is unauthorized the rules as to material
alteration apply (Section 3--407), even though the paper was not
delivered by the maker or drawer; but the burden of establishing that
any completion is unauthorized is on the party so asserting.