Create two records, each with a c field assigned the NULL value.
Because the c field is NULL, the verification record(expand), which is needed to compare the a fields, returns false.
Use the verification Or(expand,%NULL) to verify the records.
The seq verifier may also be used for this, because a NULL value matches an empty sequence.
Use the &, operator to verify an expression sequence assigned to a record.
Using any of the special verifications outside a mutable structure verifier returns FAIL.