SetPlaceholder is invalid and does not display placeholders

`
<CodeArea fx:id="result3" prefWidth="300" preHeight="300"/>
`

```
@FXML
private CodeArea result3;

@FXML
void initialize() throws IOException {
    TextFlow placeholder = new TextFlow (new Text ("myText"));
    result3.setPlaceholder(placeholder, Pos.CENTER);
}
```

Do not display placeholder characters，Why is this? Did I make a spelling mistake？