Converts `func` to its source code.

@private
@param {Function} func The function to convert.
@returns {string} Returns the source code.
function toSource$4(func) {
	  if (func != null) {
	    try {
	      return funcToString$5.call(func);
	    } catch (e) {}
	    try {
	      return (func + '');
	    } catch (e) {}
	  }
	  return '';
	}