feat: tea.Batch returns nil if all cmds are nil (#217)

Signed-off-by: Carlos A Becker <caarlos0@gmail.com>

commands_test.go

@@ -80,3 +80,28 @@ func TestSequentially(t *testing.T) {
 		})
 	}
 }
+
+func TestBatch(t *testing.T) {
+	t.Run("nil cmd", func(t *testing.T) {
+		if b := Batch(nil); b != nil {
+			t.Fatalf("expected nil, got %+v", b)
+		}
+	})
+	t.Run("empty cmd", func(t *testing.T) {
+		if b := Batch(); b != nil {
+			t.Fatalf("expected nil, got %+v", b)
+		}
+	})
+	t.Run("single cmd", func(t *testing.T) {
+		b := Batch(Quit)()
+		if l := len(b.(batchMsg)); l != 1 {
+			t.Fatalf("expected a []Cmd with len 1, got %d", l)
+		}
+	})
+	t.Run("mixed nil cmds", func(t *testing.T) {
+		b := Batch(nil, Quit, nil, Quit, nil, nil)()
+		if l := len(b.(batchMsg)); l != 2 {
+			t.Fatalf("expected a []Cmd with len 2, got %d", l)
+		}
+	})
+}