core: fix warnings in error

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --git a/lib/core/error.nit b/lib/core/error.nit
index ac13301..6a58480 100644 (file)
--- a/lib/core/error.nit
+++ b/lib/core/error.nit
@@ -86,6 +86,6 @@ class MaybeError[V, E: Error]
        redef fun to_s do
                var e = maybe_error
                if e != null then return e.to_s
-               return value.to_s
+               return value.as(not null).to_s
        end
 end