java: don't crash on `to_s` when not null in Nit (even if null in Java)

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/lib/java/ffi_support.nit b/lib/java/ffi_support.nit
index 0a1e4bf..cadb598 100644 (file)
--- a/lib/java/ffi_support.nit
+++ b/lib/java/ffi_support.nit
@@ -29,8 +29,9 @@ redef class Sys
        private var jvm_cache: nullable JavaVM = null
        private var jni_env_cache: nullable JniEnv = null
 
-       # Default Java Virtual Machine to use (will be instantiated using
-       # `create_default_jvm` if not already set)
+       # Default Java Virtual Machine to use
+       #
+       # Instantiated using `create_default_jvm` if not already set.
        fun jvm: JavaVM
        do
                if jvm_cache == null then create_default_jvm
@@ -110,7 +111,11 @@ extern class JavaString in "Java" `{ java.lang.String `}
                return nit_cstr;
        `}
 
-       redef fun to_s do return to_cstring.to_s
+       redef fun to_s
+       do
+               if is_java_null then return "<{inspect_head}:null>"
+               return to_cstring.to_s
+       end
 end
 
 redef class NativeString
@@ -188,7 +193,7 @@ redef extern class JavaObject
        # Use Java's `toString` for any `JavaObject`
        redef fun to_s
        do
-               if is_java_null then return super
+               if is_java_null then return "<{inspect_head}:null>"
                return to_java_string.to_s
        end
 end