unable to escape htl expression

the spec states:

> Like in JSP (see section "1.2.2 Literal-expression" from the JSP 2.1 Expression Language Specification), to escape an expression (the `${)`, it can be prefixed it with a backslash `\${)`).

but this doesn't work:

```
${"

" @ context = "text"}
```

gives:

```
TypeError: Cannot destructure property `plugin` of 'undefined' or 'null'.
```

workaround: use unicode escape:

```
${"

" @ context = "text"}
```