Minor documentation fixes

- Updated InvoiceTotals class
- Updated Invoice class
- Updated AllowanceOrCharge class
- Updated CONTRIBUTING.md

CONTRIBUTING.md

@@ -19,17 +19,17 @@ The main repository branch is only for stable releases.
 
 ### 2. Passes static analysis inspection
 ```
-vendor/bin/phan --testdox
+vendor/bin/phan --allow-polyfill-parser
 ```
 
 ### 3. Passes all tests
 ```
-vendor/bin/simple-phpunit
+vendor/bin/simple-phpunit --testdox
 ```
 
 ### 4. Complies with EN 16931
 Although the most popular European Invoicing CIUS is [PEPPOL BIS Billing 3.0](https://docs.peppol.eu/poacc/billing/3.0/),
-the real deal is the "European Standard for Electronic invocing" or EN 16931.
+the real deal is the "European Standard for Electronic invoicing" or EN 16931.
 
 This means that, while most users will use the [Peppol](src/Presets/Peppol.php) preset for reading and writing invoices,
 there are other CIUS/extensions from various member states and business sectors which might not be an exact match to PEPPOL.

src/AllowanceOrCharge.php

@@ -6,7 +6,7 @@
 class AllowanceOrCharge {
  protected $reasonCode = null;
  protected $reason = null;
- protected $amount = null;
+ protected $amount = 0;
  protected $isPercentage = false;
 
  use VatTrait;

src/Invoice.php

@@ -134,7 +134,7 @@ class Invoice {
  /**
  * Forwarder's invoice discrepancy report
  *
- * Document/message reporting invoice discrepancies indentified by the forwarder.
+ * Document/message reporting invoice discrepancies identified by the forwarder.
  */
  const TYPE_FORWARDERS_INVOICE_DISCREPANCY_REPORT = 553;
 

src/Models/InvoiceTotals.php

@@ -160,10 +160,10 @@ static public function fromInvoice(Invoice $inv): InvoiceTotals {
 
  /**
  * Update VAT map
- * @param VatBreakdown[string] &$vatMap VAT map reference
- * @param VatTrait $item Item instance
- * @param float|null $rate VAT rate
- * @param float $addTaxableAmount Taxable amount to add
+ * @param array<string,VatBreakdown> &$vatMap VAT map reference
+ * @param VatTrait  $item Item instance
+ * @param float|null  $rate VAT rate
+ * @param float  $addTaxableAmount Taxable amount to add
  */
  static private function updateVatMap(array &$vatMap, $item, float $addTaxableAmount) {
  $category = $item->getVatCategory();