Use mb_convert_encoding when encoding detected, else try utf8_encode

src/Request.php

@@ -132,9 +132,7 @@ public function request($access, $request, $endpointurl)
             ]);
 
             if ($response->getStatusCode() === 200) {
-                if (function_exists('mb_convert_encoding')) {
-                    $body = mb_convert_encoding($body, 'UTF-8', mb_detect_encoding($body));
-                }
+                $body = $this->convertEncoding($body);
 
                 $xml = new SimpleXMLElement($body);
                 if (isset($xml->Response) && isset($xml->Response->ResponseStatusCode)) {
@@ -218,4 +216,22 @@ public function getEndpointUrl()
     {
         return $this->endpointUrl;
     }
+
+    /**
+     * @param $body
+     * @return string
+     */
+    protected function convertEncoding($body)
+    {
+        if (!function_exists('mb_convert_encoding')) {
+            return $body;
+        }
+
+        $encoding = mb_detect_encoding($body);
+        if ($encoding) {
+            return mb_convert_encoding($body, 'UTF-8', $encoding);
+        }
+
+        return utf8_encode($body);
+    }
 }

tests/Ups/Tests/EntityTest.php

@@ -192,5 +192,4 @@ public function getListOfNodesWithoutNodeInterface()
             return [$item];
         }, $this->nodeListNoNodeInterface);
     }
-
 }

tests/Ups/Tests/ExceptionTest.php

@@ -6,7 +6,6 @@
 
 class ExceptionTest extends PHPUnit_Framework_TestCase
 {
-
     public function testInvalidResponseException()
     {
         $exception = new InvalidResponseException('Test Message', 1);
@@ -24,5 +23,4 @@ public function testRequestException()
         $this->assertEquals('Test Message', $exception->getMessage());
         $this->assertEquals(1, $exception->getCode());
     }
-
 }