Before advertising a route, BGP checks for its existence in the routing table. You can configure BGP to advertise a stable route, which does not need to exist in the routing table.
By configuring a static BGP4 network, you creating a stable network in the core. Although a static route does not flap unless it is manually deleted, a static BGP4 network does not interrupt the normal BGP4 decision process on other learned routes that are installed into the Routing Table Manager (RTM). Consequently, any route that can be resolved is installed into the RTM.
When the configured route is lost, BGP installs the "null0" route in the routing table. The null0 route is removed when the route is resolved.