prevHash property
PrevHash is the hash of record seq-1, which is what links the rows into a chain: a deleted or reordered record breaks the recomputation at that point. The first record of a chain carries 64 zeros rather than an empty string, so "start of chain" and "field missing" cannot look alike.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
String? prevHash;