Add psalm to require dev and initial run

composer.json

@@ -18,7 +18,8 @@
     "require-dev": {
         "nyholm/psr7": "^1.0",
         "codeception/codeception": "^5.0",
-        "codeception/module-asserts": "*"
+        "codeception/module-asserts": "*",
+        "vimeo/psalm": "^5"
     },
     "autoload": {
         "psr-4": {

psalm.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0"?>
+<psalm
+    errorLevel="4"
+    resolveFromConfigFile="true"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
+    findUnusedBaselineEntry="true"
+    findUnusedCode="true"
+>
+    <projectFiles>
+        <directory name="src" />
+        <ignoreFiles>
+            <directory name="vendor" />
+        </ignoreFiles>
+    </projectFiles>
+    <issueHandlers>
+        <!-- This set can be removed by adding psalm-api tags -->
+        <PossiblyUnusedMethod errorLevel="suppress"/>
+        <PossiblyUnusedProperty errorLevel="suppress"/>
+        <UnusedClass errorLevel="suppress"/>
+    </issueHandlers>
+</psalm>

src/Extensions/ExceptionReporter.php

@@ -350,7 +350,7 @@ protected function getParameterNames(ReflectionFunctionAbstract $reflection): ar
      *
      * @param mixed[] $values raw PHP values
      *
-     * @return string[] formatted values
+     * @return list<string> formatted values
      */
     protected function formatValues(array $values): array
     {

src/Model/Breadcrumb.php

@@ -44,6 +44,10 @@ public function __construct(int $timestamp, string $level, string $message, arra
      */
     public function jsonSerialize(): array
     {
-        return array_filter(get_object_vars($this));
+		// Avoids a psalm error for unused property on "data"
+		$out = array_merge(get_object_vars($this), [
+			'data' => $this->data,
+		]);
+        return array_filter($out);
     }
 }

src/Model/Request.php

@@ -25,9 +25,9 @@ class Request implements JsonSerializable
     public $query_string;
 
     /**
-     * @var string|null cookie values (unparsed, as a string)
+     * @var array cookie values (unparsed, as a string)
      */
-    public $cookies;
+    public $cookies = [];
 
     /**
      * @var string[] map where header-name => header-value