Fix error message from KeyForObj when passing an invalid struct.

filter/dscache/ds.go

Index: filter/dscache/ds.go
diff --git a/filter/dscache/ds.go b/filter/dscache/ds.go
index 36b308e4644e4ad7d7a2c0016ae04a31e311fded..e1495e8a0a56fafbed7efcfaca0da85d1067e499 100644
--- a/filter/dscache/ds.go
+++ b/filter/dscache/ds.go
@@ -87,7 +87,13 @@ func (d *dsCache) GetMulti(keys []*ds.Key, metas ds.MultiMetaGetter, cb ds.GetMu
 
 			if toSave != nil {
 				if shouldSave { // save
-					expSecs := metas.GetMetaDefault(i, CacheExpirationMeta, CacheTimeSeconds).(int64)
+					mg := metas.GetSingle(i)
+					v, err := ds.GetMetaDefault(mg, CacheExpirationMeta, CacheTimeSeconds)
+					if err != nil {
+						// TODO(riannucci): Not sure what to do with this.

[iannucci, 2015/12/12 03:52:22]

as in; this should basically never happen, but if it does happen, we should know
about it. Plumbing it through in this function as it's written right now is
going to be a pain in the butt :/

+						panic(err)
+					}
+					expSecs := v.(int64)
 					toSave.SetFlags(uint32(ItemHasData))
 					toSave.SetExpiration(time.Duration(expSecs) * time.Second)
 					toSave.SetValue(data)