panic with `AsString()` on result of json encoding of to_number conversion of null value about go-cty HOT 4 CLOSED

func (f Function) Call(args []cty.Value) (val cty.Value, err error) {
	expectedType, dynTypeArgs, err := f.returnTypeForValues(args)
	if err != nil {
		return cty.NilVal, err
	}
	if dynTypeArgs {
		// returnTypeForValues sets this if any argument was inexactly typed
		// and the corresponding parameter did not indicate it could deal with
		// that. In that case we also avoid calling the implementation function
		// because it will also typically not be ready to deal with that case.
		return cty.UnknownVal(expectedType), nil
		       ^^^^^^^^^^^^^^
	}

func (f Function) returnTypeForValues(args []cty.Value) (ty cty.Type, dynTypedArgs bool, err error) {
...
		if val.Type() == cty.DynamicPseudoType {
			if !spec.AllowDynamicType {
				return cty.DynamicPseudoType, true, nil
			}

				AllowDynamicType: true,

func MakeToFunc(wantTy cty.Type) function.Function {
	return function.New(&function.Spec{
		Description: fmt.Sprintf("Converts the given value to %s, or raises an error if that conversion is impossible.", wantTy.FriendlyName()),
		Params: []function.Parameter{
			{
				Name: "v",
				// We use DynamicPseudoType rather than wantTy here so that
				// all values will pass through the function API verbatim and
				// we can handle the conversion logic within the Type and
				// Impl functions. This allows us to customize the error
				// messages to be more appropriate for an explicit type
				// conversion, whereas the cty function system produces
				// messages aimed at _implicit_ type conversions.
				Type:             cty.DynamicPseudoType,
				AllowNull:        true,
			},
		},