Command feedback says "Unkown command" when parameters are incomplete

The Bug

When executing a command that has missing parameters, the command feedback message will say "Unkown command" even though, the command itself is an exiting command.
A better and less confusing message would be "Missing parameters for command"

/advancement grant

When using invalid parameters, the message is already correct, then it will say "Incorrect argument for command" or similar (like expected double, depending on the parameter.)