As shown above, null subjects in LIS can occur both with plain and agreement verbs (SYNTAX 2.4.1.1). However, according to corpus data, subjects remain unexpressed more frequently with agreement verbs than with plain verbs. This behaviour has been observed in other sign languages as well.
Moreover, null subjects are likely to occur with predicate classifiers (MORPHOLOGY 5.1). Since the classifier handshape may provide information about the type, size, shape, movement, and location of the relevant referent, it might be easier for the addressee to retrieve the omitted referent. For example, if the signer is talking about the relationship between a friend of hers and her dog, a predicate classifier like the one shown below is automatically associated with the only salient two-legged entity, the signer’s friend. Under these circumstances, the subject may be omitted.
CL(V): ‘walk’
‘(She) was walking.’