diff --git a/01.workspace/heave/src/fun/sqlite_init_db.rs b/01.workspace/heave/src/fun/sqlite_init_db.rs
index 9deb235..42ca808 100644
--- a/01.workspace/heave/src/fun/sqlite_init_db.rs
+++ b/01.workspace/heave/src/fun/sqlite_init_db.rs
@@ -6,7 +6,7 @@ pub fn run(path: &path::Path) {
         CREATE TABLE IF NOT EXISTS entity (
             id TEXT PRIMARY KEY,
             class TEXT NOT NULL,
-            ref_date INTEGER NOT NULL
+            ref_date INTEGER
         );
         CREATE TABLE IF NOT EXISTS attribute (
             id TEXT,
diff --git a/01.workspace/heave/src/fun/sqlite_map_row_to_entity.rs b/01.workspace/heave/src/fun/sqlite_map_row_to_entity.rs
index 53daac1..ff6a973 100644
--- a/01.workspace/heave/src/fun/sqlite_map_row_to_entity.rs
+++ b/01.workspace/heave/src/fun/sqlite_map_row_to_entity.rs
@@ -3,11 +3,14 @@ use crate::*;
 pub fn run(row: &rusqlite::Row) -> rusqlite::Result<Entity> {
     let id: String = row.get(0)?;
     let class: String = row.get(1)?;
-    let ref_date: u64 = row.get(2)?;
-    Ok(Entity::default()
-        .with_id(&id)
-        .with_class(&class)
-        .with_ref_date(ref_date))
+    let ref_date: Option<u64> = row.get(2)?;
+    let entity = Entity {
+        id,
+        class,
+        ref_date,
+        ..Entity::default()
+    };
+    Ok(entity)
 }
 
 // #[cfg(test)]
diff --git a/01.workspace/heave/src/str/entity.rs b/01.workspace/heave/src/str/entity.rs
index 61cfa9f..f617ec8 100644
--- a/01.workspace/heave/src/str/entity.rs
+++ b/01.workspace/heave/src/str/entity.rs
@@ -4,7 +4,7 @@ use crate::*;
 pub struct O {
     pub id: String,
     pub state: EntityState,
-    pub ref_date: u64,
+    pub ref_date: Option<u64>,
     pub class: String,
     pub attributes: std::collections::HashMap<String, Attribute>,
 }
@@ -28,7 +28,7 @@ impl O {
         self
     }
     pub fn with_ref_date(mut self, ref_date: u64) -> Self {
-        self.ref_date = ref_date;
+        self.ref_date = Some(ref_date);
         self
     }
     pub fn with_attribute(mut self, id: &str, value: impl Into<Value>) -> Self {