Handle OrgDoc's ID.

org_rw/org_rw.py

@@ -1571,6 +1571,16 @@ class OrgDoc:
             map(lambda hl: parse_headline(hl, self, self), headlines)
         )
 
+    @property
+    def id(self):
+        """
+        Created by org-roam v2.
+        """
+        for p in self.properties:
+            if p.key == 'ID':
+                return p.value
+        return None
+
     @property
     def path(self):
         return self._path