[gnumeric] Introspection fix.

[Morten Welinder <mortenw src gnome org>]

commit b109a997264e03a543322d06552f5557eb1ef818
Author: Morten Welinder <terra gnome org>
Date:   Thu Jul 30 21:00:37 2020 -0400

    Introspection fix.

 src/expr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/expr.c b/src/expr.c
index 434e9b739d..64addecf52 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -2738,7 +2738,7 @@ do_expr_walk (GnmExpr const *expr, GnmExprWalkerFunc walker, GnmExprWalk *data)
  * @walker: (scope call): callback for each sub-expression
  * @user: user data pointer
  *
- * Returns: (transfer full) (allow-none): transformed expression.
+ * Returns: (transfer full) (nullable): transformed expression.
  *
  * This function walks the expression and calls the walker function for
  * each subexpression.  If the walker returns a non-%NULL expression,