118: queryRecords should return [] when no matching records exist, not an error (#121)

Whenever a key is used which doesn't exist in the DB at all, an error is returned like this:

```
[
  {
    message: `rpc error: code = Unknown desc = store doesn't have key: "\\atypeApplicationRecord"`,
    path: [ 'queryRecords' ]
  }
]
```

That doesn't make any sense, as it is not an error to find out that the thing you asked for does not exist.  This changes it to return an empty list.

Reviewed-on: #121
Reviewed-by: David Boreham <dboreham@noreply.git.vdb.to>
Co-authored-by: Thomas E Lackey <telackey@bozemanpass.com>
Co-committed-by: Thomas E Lackey <telackey@bozemanpass.com>

x/registry/keeper/keeper.go

@@ -20,6 +20,7 @@ import (
 	auth "github.com/cosmos/cosmos-sdk/x/auth/keeper"
 	bank "github.com/cosmos/cosmos-sdk/x/bank/keeper"
 	paramtypes "github.com/cosmos/cosmos-sdk/x/params/types"
+	"github.com/tendermint/tendermint/libs/log"
 )
 
 var (
@@ -96,6 +97,11 @@ func NewKeeper(cdc codec.BinaryCodec, accountKeeper auth.AccountKeeper, bankKeep
 	}
 }
 
+// Logger returns a module-specific logger.
+func (k Keeper) Logger(ctx sdk.Context) log.Logger {
+	return ctx.Logger().With("module", types.ModuleName)
+}
+
 // GetRecordIndexKey Generates Bond ID -> Bond index key.
 func GetRecordIndexKey(id string) []byte {
 	return append(PrefixCIDToRecordIndex, []byte(id)...)
@@ -389,7 +395,8 @@ func (k Keeper) GetAttributeMapping(ctx sdk.Context, key []byte) ([]string, erro
 	store := ctx.KVStore(k.storeKey)
 
 	if !store.Has(key) {
-		return nil, fmt.Errorf("store doesn't have key: %q", key)
+		k.Logger(ctx).Debug(fmt.Sprintf("store doesn't have key: %q", key))
+		return []string{}, nil
 	}
 
 	var recordIds []string