Revert "Remove redundant extra capabilities default checking"

This reverts commit 959f599c5520e5a7ba95c45cdaefbcf6e72df219.

lib/Selenium/Remote/Driver.pm

@@ -365,7 +365,7 @@ sub _execute_command {
 # desired capabilities on the server.
 sub new_session {
     my ( $self, $extra_capabilities ) = @_;
-
+    $extra_capabilities ||= {};
     my $args = {
         'desiredCapabilities' => {
             'browserName'       => $self->browser_name,