fix(js): unpack guregu/null value when setting script options

Closes #886

js/bundle.go

@@ -27,6 +27,7 @@ import (
 	"runtime"
 
 	"github.com/loadimpact/k6/lib/consts"
+	"gopkg.in/guregu/null.v3"
 
 	"github.com/dop251/goja"
 	"github.com/loadimpact/k6/js/common"
@@ -217,6 +218,18 @@ func (b *Bundle) Instantiate() (bi *BundleInstance, instErr error) {
 		jsOptionsObj = jsOptions.ToObject(rt)
 	}
 	b.Options.ForEachSpecified("json", func(key string, val interface{}) {
+		switch v := val.(type) {
+		case null.Bool:
+			val = v.ValueOrZero()
+		case null.Float:
+			val = v.ValueOrZero()
+		case null.Int:
+			val = v.ValueOrZero()
+		case null.String:
+			val = v.ValueOrZero()
+		case null.Time:
+			val = v.ValueOrZero()
+		}
 		if err := jsOptionsObj.Set(key, val); err != nil {
 			instErr = err
 		}

js/bundle_test.go

@@ -588,6 +588,9 @@ func TestOpen(t *testing.T) {
 
 func TestBundleInstantiate(t *testing.T) {
 	b, err := getSimpleBundle("/script.js", `
+		export let options = {
+			vus: 5,
+		};
 		let val = true;
 		export default function() { return val; }
 	`)
@@ -614,6 +617,13 @@ func TestBundleInstantiate(t *testing.T) {
 			assert.Equal(t, false, v.Export())
 		}
 	})
+
+	t.Run("Options", func(t *testing.T) {
+		// Ensure `options` properties are correctly marshalled
+		jsOptions := bi.Runtime.Get("options").ToObject(bi.Runtime)
+		val := jsOptions.Get("vus").Export()
+		assert.Equal(t, int64(5), val)
+	})
 }
 
 func TestBundleEnv(t *testing.T) {