Ezp 22997 - Incorrect code documentation for method ContentService.prototype.loadContent()

Corrected params' default values of method `ContentService.prototype.loadContent()` to any avoid any issues with incorrect concatenation of null-valued params.
Improved code documentation for `ContentService.prototype.loadContent()` method by adding information about params' default values.
you should maybe update the example above to use empty strings instead of `null`