Write empty tables as well (#169)

Empty tables are allowed by the spec, so they should not be removed:

  [[empty-tables]]
  [[empty-tables]]

is perfectly valid.

Fixes #163

tomltree_write.go

@@ -142,18 +142,16 @@ func (t *Tree) writeTo(w io.Writer, indent, keyspace string, bytesCount int64) (
 			}
 		case []*Tree:
 			for _, subTree := range node {
-				if len(subTree.values) > 0 {
-					tableArrayName := fmt.Sprintf("\n%s[[%s]]\n", indent, combinedKey)
-					writtenBytesCount, err := w.Write([]byte(tableArrayName))
-					bytesCount += int64(writtenBytesCount)
-					if err != nil {
-						return bytesCount, err
-					}
+				tableArrayName := fmt.Sprintf("\n%s[[%s]]\n", indent, combinedKey)
+				writtenBytesCount, err := w.Write([]byte(tableArrayName))
+				bytesCount += int64(writtenBytesCount)
+				if err != nil {
+					return bytesCount, err
+				}
 
-					bytesCount, err = subTree.writeTo(w, indent+"  ", combinedKey, bytesCount)
-					if err != nil {
-						return bytesCount, err
-					}
+				bytesCount, err = subTree.writeTo(w, indent+"  ", combinedKey, bytesCount)
+				if err != nil {
+					return bytesCount, err
 				}
 			}
 		}

tomltree_write_test.go

@@ -40,6 +40,30 @@ func assertErrorString(t *testing.T, expected string, err error) {
 	}
 }
 
+func TestTreeWriteToEmptyTable(t *testing.T) {
+	doc := `[[empty-tables]]
+[[empty-tables]]`
+
+	toml, err := Load(doc)
+	if err != nil {
+		t.Fatal("Unexpected Load error:", err)
+	}
+	tomlString, err := toml.ToTomlString()
+	if err != nil {
+		t.Fatal("Unexpected ToTomlString error:", err)
+	}
+
+	expected := `
+[[empty-tables]]
+
+[[empty-tables]]
+`
+
+	if tomlString != expected {
+		t.Fatalf("Expected:\n%s\nGot:\n%s", expected, tomlString)
+	}
+}
+
 func TestTreeWriteToTomlString(t *testing.T) {
 	toml, err := Load(`name = { first = "Tom", last = "Preston-Werner" }
 points = { x = 1, y = 2 }`)