Handle case of no tag given for invoice

In that case, strings.Split() return an array with a single empty string
element, that does not pass the domain check for tag_name in the
database.

And an invoice with no tags would get an array of a single NULL in
array_agg, so i had to convert it to an empty string in order for it
to work as expected.

pkg/invoices.go

@@ -56,7 +56,7 @@ func mustCollectInvoiceEntries(ctx context.Context, conn *Conn, company *Company
 		     , invoice_number
 		     , contact.business_name
 		     , contact.slug
-		     , array_agg(tag.name::text)
+		     , array_agg(coalesce(tag.name::text, ''))
 		     , invoice.invoice_status
 		     , isi18n.name
 		     , to_price(total, decimal_digits)
@@ -609,7 +609,11 @@ func mustGetTaxOptions(ctx context.Context, conn *Conn, company *Company) []*Sel
 
 func (form *invoiceForm) SplitTags() []string {
 	reg := regexp.MustCompile("[^a-z0-9-]+")
-	return strings.Split(reg.ReplaceAllString(form.Tags.Val, " "), " ")
+	tags := strings.Split(reg.ReplaceAllString(form.Tags.Val, ","), ",")
+	if len(tags) == 1 && len(tags[0]) == 0 {
+		return []string{}
+	}
+	return tags
 }
 
 type invoiceProductForm struct {