Steps to replicate the issue (include links if applicable):

• Create an extension with a parser function.
• Set the return value for the parser function to [] (or anything without a text or 0-indexed parameter)
• Use the new function on a page.

What happens?:
No error is generated immediately; instead, braceSubstitution() starts popping up Undefined index: text notices with no indication as to the actual cause of the problem.

What should have happened instead?:
Either the situation should have been handled gracefully, in a similar fashion to handling an empty string, or an error message should have been generated at the site of the actual problem.

Other information (browser name/version, screenshots, etc.):
If graceful handling is preferred, I believe replacing the code towards the end of callParserFunction() with the following should do the trick:

if (!is_array($result)) {
	...
} else {
	if (!isset($result['text'])) {
		if (isset($result[0])) {
			$result['text'] = $result[0];
			unset($result[0]);
		} else {
			$result['text'] = '';
		}
	}
	...
}