Empty value for optional JSX property causing exception in transpiler

[mor-n4]

Exception:

Severe error occurred in transpiler=es message=element to process may not be null.
java.lang.IllegalArgumentException: element to process may not be null
	at org.eclipse.n4js.transpiler.print.PrettyPrinterEcmaScript.process(PrettyPrinterEcmaScript.java:1257)
	at org.eclipse.n4js.transpiler.print.PrettyPrinterEcmaScript.caseParenExpression(PrettyPrinterEcmaScript.java:691)
	at org.eclipse.n4js.transpiler.print.PrettyPrinterEcmaScript.caseParenExpression(PrettyPrinterEcmaScript.java:1)
	at org.eclipse.n4js.n4JS.util.N4JSSwitch.doSwitch(N4JSSwitch.java:745)
	at org.eclipse.n4js.transpiler.print.PrettyPrinterEcmaScript.doSwitch(PrettyPrinterEcmaScript.java:82)
	at org.eclipse.n4js.transpiler.print.PrettyPrinterEcmaScript.doSwitch(PrettyPrinterEcmaScript.java:1)
	at org.eclipse.emf.ecore.util.Switch.doSwitch(Switch.java:53)
	at org.eclipse.n4js.transpiler.print.PrettyPrinterEcmaScript.doSwitch(PrettyPrinterEcmaScript.java:75)
	at org.eclipse.n4js.transpiler.print.PrettyPrinterEcmaScript.doSwitch(PrettyPrinterEcmaScript.java:1)
	at org.eclipse.emf.ecore.util.Switch.doSwitch(Switch.java:69)

To reproduce:

import * as React from "react";

export public interface ~MyProps {
    public header?: React.ReactElement<?>;
}

export public function MyElement(props: MyProps): React.ReactElement<?> {
	return null;
}


let elem = <MyElement header={(
)}>

</MyElement>;

Note: if the line break after let elem = <MyElement header={( is removed, a syntax error is shown.

[mor-n4]

This seems to be a bug in the parser: it seems to accept empty parenthesis expression if they contain a line break.

The above exception can be reproduced with the following code:

let x = (
);

When removing the line break, the parser correctly emits a syntax error:

let x = (); // error: no viable alternative at input ')'

(BTW: if this is true, it makes sense that the transpiler throws an exception.)