[Zope] Creating product with Python

When I trying create an instance of class of my own product "Boring" with Python, Zope tells me: Missing doc string at: http://localhost:8080/a/manage_addProduct/Boring/manage_addBoring I tried to change "manage_addBoring" method, and compared my product with other working products, by there was no results from my attemptions. What that Error message means?