Fix error message from KeyForObj when passing an invalid struct.

service/datastore/raw_interface_test.go

Index: service/datastore/raw_interface_test.go
diff --git a/service/datastore/raw_interface_test.go b/service/datastore/raw_interface_test.go
index 475d16af72ea34f71b8cd5eb6e8db19fe29b5c42..f8201001413f41e81a0dc7074d5da8beef8e0845 100644
--- a/service/datastore/raw_interface_test.go
+++ b/service/datastore/raw_interface_test.go
@@ -20,13 +20,18 @@ func TestMultiMetaGetter(t *testing.T) {
 			So(err, ShouldEqual, ErrMetaFieldUnset)
 			So(val, ShouldBeNil)
 
-			So(mmg.GetMetaDefault(7, "hi", "value"), ShouldEqual, "value")
+			v, err := GetMetaDefault(mmg.GetSingle(7), "hi", "value")
+			So(err, ShouldBeNil)
+			So(v, ShouldEqual, "value")
 
 			m := mmg.GetSingle(10)
 			val, err = m.GetMeta("hi")
 			So(err, ShouldEqual, ErrMetaFieldUnset)
 			So(val, ShouldBeNil)
-			So(m.GetMetaDefault("hi", "value"), ShouldEqual, "value")
+
+			v, err = GetMetaDefault(m, "hi", "value")
+			So(err, ShouldBeNil)
+			So(v, ShouldEqual, "value")
 		})
 
 		Convey("stuff", func() {
@@ -36,16 +41,22 @@ func TestMultiMetaGetter(t *testing.T) {
 			mmg := NewMultiMetaGetter(pmaps)
 
 			// oob is OK
-			So(mmg.GetMetaDefault(7, "hi", "value"), ShouldEqual, "value")
+			v, err := GetMetaDefault(mmg.GetSingle(7), "hi", "value")
+			So(err, ShouldBeNil)
+			So(v, ShouldEqual, "value")
 
 			// nil is OK
-			So(mmg.GetMetaDefault(1, "key", true), ShouldEqual, true)
+			v, err = GetMetaDefault(mmg.GetSingle(1), "key", true)
+			So(err, ShouldBeNil)
+			So(v, ShouldEqual, true)
 
 			val, err := mmg.GetMeta(0, "hi")
 			So(err, ShouldBeNil)
 			So(val, ShouldEqual, "thing")
 
-			So(mmg.GetMetaDefault(2, "key", 20), ShouldEqual, 100)
+			v, err = GetMetaDefault(mmg.GetSingle(2), "key", 20)
+			So(err, ShouldBeNil)
+			So(v, ShouldEqual, 100)
 		})
 	})
 }