Validate value object required fields in the constructor (#1488)

* Refactor the code generating object properties

* Refactor the generation of array getters

Optional array fields still need to consider the property as nullable
even though the getter will return an empty array as AWS does not treat
absent lists the same than empty lists in input.

* Add validation of required parameters in value object constructors

* Remove checks for missing properties for value object request bodies

This is already validated in the constructor now.

Author: stof

src/ValueObject/Record.php

@@ -22,7 +22,7 @@ final class Record
      */
     public function __construct(array $input)
     {
-        $this->data = $input['Data'] ?? null;
+        $this->data = $input['Data'] ?? $this->throwException(new InvalidArgument('Missing required field "Data".'));
     }
 
     /**
@@ -46,11 +46,17 @@ public function getData(): string
     public function requestBody(): array
     {
         $payload = [];
-        if (null === $v = $this->data) {
-            throw new InvalidArgument(sprintf('Missing parameter "Data" for "%s". The value cannot be null.', __CLASS__));
-        }
+        $v = $this->data;
         $payload['Data'] = base64_encode($v);
 
         return $payload;
     }
+
+    /**
+     * @return never
+     */
+    private function throwException(\Throwable $exception)
+    {
+        throw $exception;
+    }
 }