counter: fix NPE on nullable element to_s

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

diff --git a/lib/counter.nit b/lib/counter.nit
index ceecb48..ceb9896 100644 (file)
--- a/lib/counter.nit
+++ b/lib/counter.nit
@@ -133,6 +133,7 @@ class Counter[E]
        # @toimplement by default just call `to_s` on the element
        protected fun element_to_s(e: E): String
        do
+               if e == null then return "null"
                return e.to_s
        end