Fix getAttributeDescription() error (#264)

* test: Add a test to check getDescription() return value for invalid value

* fix: Avoid error if value is invalid

Author: PortableSteve

src/Enum.php

@@ -403,6 +403,9 @@ protected static function getAttributeDescription($value): ?string
         $reflection = self::getReflection();
         $constantName = static::getKey($value);
         $constReflection = $reflection->getReflectionConstant($constantName);
+        if ($constReflection === false) {
+            return null;
+        }
         $descriptionAttributes = $constReflection->getAttributes(Description::class);
 
         if (count($descriptionAttributes) === 1) {

tests/EnumAttributeDescriptionTest.php

@@ -25,4 +25,9 @@ public function test_an_exception_is_thrown_when_accessing_a_description_which_i
 
         DescriptionFromAttribute::InvalidCaseWithMultipleDescriptions()->description;
     }
+
+    public function test_an_exception_is_not_thrown_when_accessing_a_description_for_an_invalid_value()
+    {
+        $this->assertSame('', DescriptionFromAttribute::getDescription('invalid'));
+    }
 }