Validate two optional fields which should only be validated together

[makks129]

I have a struct with 2 fields: latitude and longitude
Both of them are optional, but if 1 is present the other should be validated as required
I haven't found a combination that would work to validate these 4 cases:

1.
lat=nil
lng=nil
Valid
2.
lat=123
lng=nil
Error
3.
lat=nil
lng=123
Error
4.
lat=123
lng=123
Valid

I tried different variations of required_ and excluded_ and omitempty but one of the cases always failed so far

Lat         string  `json:"lat" validate:"required_with=Inner.Lng,excluded_without=Inner.Lng,omitempty,latitude"`
Lng         string  `json:"lng" validate:"required_with=Inner.Lat,excluded_without=Inner.Lat,omitempty,longitude"`

It seems that it should be a fairly common case. Your help will be greatly appreciated!