Runtime error: assignment to entry in nil map

You are trying to create a slice of maps; consider the following example:

http://play.golang.org/p/gChfTgtmN-

package main

import "fmt"

func main() {
    a := make([]map[string]int, 100)
    for i := 0; i < 100; i++ {
        a[i] = map[string]int{"id": i, "investor": i}
    }
    fmt.Println(a)
}

You can rewrite these lines:

invs[i] = make(map[string]string)
invs[i]["Id"] = inv_ids[i]
invs[i]["Investor"] = inv_names[i]

as:

invs[i] = map[string]string{"Id": inv_ids[i], "Investor": inv_names[i]}

this is called a composite literal.

Now, in a more idiomatic program, you'd most probably want to use a struct to represent an investor:

http://play.golang.org/p/vppK6y-c8g

package main

import (
    "fmt"
    "strconv"
)

type Investor struct {
    Id   int
    Name string
}

func main() {
    a := make([]Investor, 100)
    for i := 0; i < 100; i++ {
        a[i] = Investor{Id: i, Name: "John" + strconv.Itoa(i)}
        fmt.Printf("%#v\n", a[i])
    }
}