Fix marshaling params for 'createInvoiceLink' method

Author: OvyFlash

configs.go

@@ -2117,7 +2117,12 @@ func (config InvoiceLinkConfig) params() (Params, error) {
 
 	params.AddNonEmpty("provider_token", config.ProviderToken)
 	params.AddNonZero("max_tip_amount", config.MaxTipAmount)
-	err := params.AddInterface("suggested_tip_amounts", config.SuggestedTipAmounts)
+	if len(config.SuggestedTipAmounts) > 0 {
+		err := params.AddInterface("suggested_tip_amounts", config.SuggestedTipAmounts)
+		if err != nil {
+			return params, err
+		}
+	}
 	params.AddNonEmpty("provider_data", config.ProviderData)
 	params.AddNonEmpty("photo_url", config.PhotoURL)
 	params.AddNonZero("photo_size", config.PhotoSize)
@@ -2131,7 +2136,7 @@ func (config InvoiceLinkConfig) params() (Params, error) {
 	params.AddBool("send_email_to_provider", config.SendEmailToProvider)
 	params.AddBool("is_flexible", config.IsFlexible)
 
-	return params, err
+	return params, nil
 }
 
 func (config InvoiceLinkConfig) method() string {