Check if eval buffer is empty.

Signed-off-by: kuba-- <kuba@sourced.tech>
src-d · ajnavarro · Oct 23, 2018 · Oct 22, 2018 · Oct 22, 2018 · 1c3037c63d4bbcc889e0e4e57a28497e6afe3a37
commit 1c3037c63d4bbcc889e0e4e57a28497e6afe3a37
@@ -394,7 +394,10 @@ func evalBuffer(
 	case *expression.Alias:
 		return evalBuffer(ctx, n.Child, buffer)
 	case *expression.GetField:
-		return buffer[0], nil
+		if len(buffer) > 0 {
+			return buffer[0], nil
+		}
+		return nil, nil
 	default:
 		return nil, ErrGroupBy.New(n.String())
 	}

@@ -96,6 +96,15 @@ func TestGroupBy_RowIter(t *testing.T) {
 	require.Equal(sql.NewRow("col1_2", int64(4444)), rows[1])
 }
 
+func TestGroupBy_EvalEmptyBuffer(t *testing.T) {
+	require := require.New(t)
+	ctx := sql.NewEmptyContext()
+
+	r, err := evalBuffer(ctx, expression.NewGetField(0, sql.Text, "col1", true), sql.Row{})
+	require.NoError(err)
+	require.Nil(r)
+}
+
 func TestGroupBy_Error(t *testing.T) {
 	require := require.New(t)
 	ctx := sql.NewEmptyContext()