Allow nil arguments for function

It uses reflect value for interface when argument is resolved as nil.

functions.go

@@ -104,7 +104,9 @@ func createCallArguments(ctx context.Context, t reflect.Type, args []interface{}
  inType = t.In(numIn - 1).Elem()
  }
  argVal := reflect.ValueOf(arg)
- if arg == nil || !argVal.Type().AssignableTo(inType) {
+ if arg == nil {
+ argVal = reflect.ValueOf(reflect.Interface)
+ } else if !argVal.Type().AssignableTo(inType) {
  return nil, fmt.Errorf("expected type %s for parameter %d but got %T",
  inType.String(), i, arg)
  }

functions_test.go

@@ -130,6 +130,17 @@ func Test_toFunc(t *testing.T) {
  },
  wantErr: context.DeadlineExceeded,
  },
+ {
+ name: "nil arg",
+ function: func(a interface{}) bool {
+ if a != nil {
+ return true
+ }
+ return false
+ },
+ arguments: []interface{}{nil},
+ want: true,
+ },
  }
  for _, tt := range tests {
  t.Run(tt.name, func(t *testing.T) {