Date Range Filter example not working

Hi all,

I am trying to follow the example for the Date Range Filter provided and can't seem to get it to work:

I've edited the .ts file and added the line

return 'OrderDate ge ${this.getUTCString(start)} and OrderDate le ${this.getUTCString(end)}';

But when it encounters this line in the browser I get a Bad Request 400 error and drilling down uncovers "The query specified in the URI is not valid. Syntax error at position 66". Some tweaking of various parts of the command seem to indicate it's unhappy with the ${} syntax, but nothing I've changed it to has worked. Any ideas?

Just tested and it works normally: