How to set a struct member that is a pointer to a string using reflection in Go

I am trying to use reflection to set a pointer. elasticbeanstalk.CreateEnvironmentInput has a field SolutionStackName which is of type *string. I am getting the following error when I try to set any value:

panic: reflect: call of reflect.Value.SetPointer on ptr Value

Here is my code:

    ...
newEnvCnf := new(elasticbeanstalk.CreateEnvironmentInput)
checkConfig2(newEnvCnf, "SolutionStackName", "teststring")
    ...
func checkConfig2(cnf interface{}, key string, value string) bool {
    log.Infof("key %v, value %s", key, value)

    v := reflect.ValueOf(cnf).Elem()
    fld := v.FieldByName(key)

    if fld.IsValid() {
        if fld.IsNil() && fld.CanSet() {
            fld.SetPointer(unsafe.Pointer(aws.String(value)))
//aws.String returns a pointer

...

Here is the log output

time="2016-02-20T23:54:52-08:00" level=info msg="key [SolutionStackName], value teststring" 
    panic: reflect: call of reflect.Value.SetPointer on ptr Value [recovered]
        panic: reflect: call of reflect.Value.SetPointer on ptr Value