it's not a valid command so it will be rejected because the only value after the mask is the administrative distance which is an integer between 1 and 255.
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This is from a running configuration and I believe it is refrencing the null0 interface but haven't found any documentation to verify that.
So the command is a valid command but does it equal to:
ip route 10.0.0.0 255.255.255.0 null 0
Is it safe to assume in this situation that if the route to 10.0.0.0 is to go to the default gateway, that you could just simply remove this route and have the same net effect? (assuming a default route exists).
If there's a shorter prefix (say 10.0.0.0/8) with a different next hop, the 10.0.0.0/24 may be an attempt to create an exception. So removing it could actually have an ill effect.
Interesting. I get the message "%Invalid next hop, looping back to the network", but the route is still inserted into the routing table and obviously the recursive lookup works anyway.