Adds validation to withParsedBody()

Per the PSR-7 spec, should only allow arrays, objects, or null values.

Author: weierophinney

src/ServerRequest.php

@@ -180,6 +180,14 @@ public function getParsedBody()
      */
     public function withParsedBody($data)
     {
+        if (! is_array($data) && ! is_object($data) && null !== $data) {
+            throw new InvalidArgumentException(sprintf(
+                '%s expects a null, array, or object argument; received %s',
+                __METHOD__,
+                gettype($data)
+            ));
+        }
+
         $new = clone $this;
         $new->parsedBody = $data;
         return $new;