readsAsOption function
Whether git, launched without a shell, would read token as one of its
own options because it starts with the - marker.
Revision expressions handed to an operation go through this gate before
git runs: one that starts with - names no revision and the operation
refuses before any command runs — a GitUnknownRevisionException where
the operation raises that exception, null where it documents a null
result.
Implementation
bool readsAsOption(String token) => token.startsWith('-');