Go: Handler crashed with error reflect: Call with too few input arguments

I want use a controller to implement a set with three functions:union, intersection and subtraction. I write a function to receive two string from POST:

func (c * SetController) Post(){
  Slice1 := c.GetString("Slice1)
  Slice2 := c.GetString("Slice2)
}

Then I write a union function to get the union set answer:

func (c *SetController) Union(Slice1 string, Slice2 string) {
    var temp1 []string = strings.Split(Slice1, ",")
    var temp2 []string = strings.Split(Slice2, ",")
    myslice1 := make([]int, 0)
    for x,_ := range temp1 {
        myslice1 = append(myslice1, x)
    }
    myslice2 := make([]int, 0)
    for x,_ := range temp2 {
        myslice2 = append(myslice2, x)
    }
    UnionAnswer := union(myslice1, myslice2)
    c.Data["UnionAnswer"] = UnionAnswer
    c.TplName = "index.tpl"
}

But after I upload the data:

curl -X POST "http://localhost:8080/?Slice1=1,3,5,6&Slice2=2,4,5,6"

and get the union answer:

curl -X GET "http://localhost:8080/getUnion"

It return a error: Handler crashed with error reflect: Call with too few input arguments

I wonder why and how to debug.