do not insist on cert to exist

sql/certificates/certs.go

@@ -59,7 +59,7 @@ func FirstInEpoch(db sql.Executor, epoch types.EpochID) (types.BlockID, error) {
 		rows   int
 	)
 	if rows, err = db.Exec(`
-		select block from certificates where layer between ?1 and ?2 and valid = 1 and block != ?3 and cert is not null
+		select block from certificates where layer between ?1 and ?2 and valid = 1 and block != ?3
 		order by layer asc limit 1;`, func(stmt *sql.Statement) {
 		stmt.BindInt64(1, int64(epoch.FirstLayer()))
 		stmt.BindInt64(2, int64((epoch+1).FirstLayer()-1))

sql/certificates/certs_test.go

@@ -171,14 +171,17 @@ func TestFirstInEpoch(t *testing.T) {
 		types.LayerID(2*layersPerEpoch - 1): {4},                // last layer of epoch 1
 		// epoch 2 has no hare output
 		types.LayerID(3 * layersPerEpoch): {5}, // first layer of epoch 3
-		// epoch 4 has hare output but no cert
+		types.LayerID(4 * layersPerEpoch): {6},
+		types.LayerID(5 * layersPerEpoch): {7},
 	}
 	for lid, bid := range lyrBlocks {
-		require.NoError(t, Add(db, lid, &types.Certificate{
-			BlockID: bid,
-		}))
+		require.NoError(t, SetHareOutput(db, lid, bid))
 	}
-	require.NoError(t, SetHareOutput(db, types.EpochID(4).FirstLayer(), types.BlockID{1, 2, 3}))
+	// epoch 4 has an invalid block
+	require.NoError(t, SetInvalid(db, types.EpochID(4).FirstLayer(), types.BlockID{6}))
+	// epoch 5 has a valid and invalid block each
+	require.NoError(t, SetHareOutput(db, types.EpochID(5).FirstLayer(), types.BlockID{1, 2, 3}))
+	require.NoError(t, SetInvalid(db, types.EpochID(5).FirstLayer(), types.BlockID{1, 2, 3}))
 
 	got, err := FirstInEpoch(db, types.EpochID(0))
 	require.NoError(t, err)
@@ -199,4 +202,8 @@ func TestFirstInEpoch(t *testing.T) {
 	got, err = FirstInEpoch(db, types.EpochID(4))
 	require.ErrorIs(t, err, sql.ErrNotFound)
 	require.Equal(t, types.EmptyBlockID, got)
+
+	got, err = FirstInEpoch(db, types.EpochID(5))
+	require.NoError(t, err)
+	require.Equal(t, types.BlockID{7}, got)
 }