fix: add missing use statement in JWK (#303)

Author: pendenga

src/JWK.php

@@ -3,6 +3,7 @@
 namespace Firebase\JWT;
 
 use DomainException;
+use InvalidArgumentException;
 use UnexpectedValueException;
 
 /**

tests/JWKTest.php

@@ -43,6 +43,20 @@ public function testParseJwkKeySet()
         self::$keys = $keys;
     }
 
+    public function testParseJwkKey_empty()
+    {
+        $this->setExpectedException('InvalidArgumentException', 'JWK must not be empty');
+
+        JWK::parseKeySet(array('keys' => array(array())));
+    }
+
+    public function testParseJwkKeySet_empty()
+    {
+        $this->setExpectedException('InvalidArgumentException', 'JWK Set did not contain any keys');
+
+        JWK::parseKeySet(array('keys' => array()));
+    }
+
     /**
      * @depends testParseJwkKeySet
      */