bug #309 Fix invalid encryption when using env (mmft24)

This PR was merged into the 3.5-dev branch.

Discussion
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Fix invalid encryption when using env

It is not possible to configure null as encryption using an environment variable. Allowing 'tcp' as configuration option would fix this issue. 'tcp' is the protocol set on the transporter wenn null is used.

Fix issue #170

Commits
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58c6b05 Fix invalid encryption when using env

Author: fabpot

DependencyInjection/SwiftmailerTransportFactory.php

@@ -144,7 +144,7 @@ public static function resolveOptions(array $options)
      */
     public static function validateConfig($options)
     {
-        if (!\in_array($options['encryption'], ['tls', 'ssl', null], true)) {
+        if (!\in_array($options['encryption'], ['tcp', 'tls', 'ssl', null], true)) {
             throw new \InvalidArgumentException(sprintf('The %s encryption is not supported', $options['encryption']));
         }