How to test FunctionImport with Edm.DateTime parameter?

Hello.

i created and implemented a FunctionImport that has an import parameter of Type Edm.DateTime. How to test this FunctionImport using the Gateway Client Transaction?

i tried to pass the value using the following options:

1.) ...&KeyDate='2015-05-12T00:00:00'

2.) ...&KeyDate=\/Date(1431416788000)\/

3.) ...&KeyDate=datetime'2015-05-12T00:00:00'

4.) ...&KeyDate=/Date(1431416788000)/

5.) ...&KeyDate=\Date(1431416788000)

6.) ...&KeyDate=2015-05-12T00:00:00

but nothing worked.

GW client alway reports the following error:

Malformed URI literal syntax

how can i pass a date to the respective import parameter using gw client in a proper way??