If at the time of evaluation a sum type still has more than one possible value, the first error-free value is taken. A value is error free if it is not an error, it is a list with only error-free elements, or it is a struct where all field values are error-free. The default value must also not be ambiguous.
In the example, replicas defaults to 1. In the case of protocol, however, there are multiple definitions with different, mutually incompatible defaults. It is still possible to resolve this error by explicitly setting the value for protocol. Try it!
// any positive number, 1 is the default replicas: 1 | uint // the default value is ambiguous protocol: "tcp" | "udp" protocol: "udp" | "tcp"
replicas: 1 protocol: _|_