[commandhandler] Giving missing field error for a struct containing private fields only

[apterf]

Problem

When defining a struct with private fields only as command data, missing field error is always thrown.

Problem is caused by private fields are skipped and default checking result is always true.
https://github.com/looplab/eventhorizon/blob/master/command.go#L159-L167

e.g. 1

type PrivateStruct struct {
	name string
	age  int
}

e.g. 2

type customTime time.Time

Suggestion

Set the default result of struct checking as false
https://github.com/looplab/eventhorizon/blob/master/command.go#L160

And suggest to use validator for custom struct:
https://github.com/looplab/eventhorizon/blob/master/middleware/commandhandler/validator/commandhandler.go

[maxekman]

Good suggestion!