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();