Revert "wip"

This reverts commit 3997bcf9.

src/linkahead/apiutils.py

@@ -550,7 +550,8 @@ def merge_entities(entity_a: Entity,
             for attribute in ("datatype", "unit", "value"):
                 if (attribute in diff_r2["properties"][key] and
                         diff_r2["properties"][key][attribute] is not None):
-                    if (diff_r1["properties"][key][attribute] is None):
+                    if (attribute not in diff_r1["properties"][key] or
+                            diff_r1["properties"][key][attribute] is None):
                         setattr(entity_a.get_property(key), attribute,
                                 diff_r2["properties"][key][attribute])
                     elif force: