store: Clarify behavior of expr_attrvalue if the attribute does not exist.

diff --git a/src/include/core/store.h b/src/include/core/store.h
index a7804ddc31f781dff833d31547a861c233f8c865..b1d15f5b77d7569e771ddd5bc5ae8741ae5f229e 100644 (file)
--- a/src/include/core/store.h
+++ b/src/include/core/store.h
@@ -320,7 +320,8 @@ sdb_store_expr_fieldvalue(int field);
 /*
  * sdb_store_expr_attrvalue:
  * Creates an expression which evaluates to the value of the specified
- * attribute of a stored object.
+ * attribute of a stored object. Evaluates to a NULL value if the attribute
+ * does not exist.
  *
  * Returns:
  *  - an expression object on success