Call method belongs to the field of the struct

I have some special type in Golang what represent a string with Validate method.

type string128 string

func (s *string128) Validate() error {
    ...
    return nil
}

There is structs have fields like the following:

type Strings1 struct {
    str1 string
    str2 string128
    str3 string128
    ...
    strN+1 string128
    strN+2 string
}

type Strings2 struct {
    str1 string
    str2 string128
    str3 string128
    ...
    strN+1 string128
    strN+2 string
}

I want to make a function where I can pass them and if the field have a Validate() function call it.

What I have done:

func validateStruct(a interface{}) error {
    v := reflect.ValueOf(a)
    t := reflect.TypeOf(a)
    for i := 0; i < v.NumField(); i++ {
        err := reflect.TypeOf(v.Field(i).Interface()).MethodByName("Validate").Call(...)
    }
    return nil
}

But it is do a lots of panic.