bugfix: get_all_DBAdaptors() should always be returning an array-ref

modules/Bio/EnsEMBL/Registry.pm

@@ -670,7 +670,7 @@ sub get_all_DBAdaptors {
   my ( $species, $group ) = rearrange( [qw(SPECIES GROUP)], @args );
 
   if ( !defined($species) && !defined($group) ) {
-    return $registry_register{'_DBA'};
+    return $registry_register{'_DBA'} || [];
   }
 
   if ( defined($species) ) {

modules/t/registry.t

@@ -36,12 +36,15 @@ else {
   note 'Using non-threaded tests';
 }
 
+my $reg = 'Bio::EnsEMBL::Registry';
+
+# Check whilst the Registry is empty
+is_deeply($reg->get_all_DBAdaptors(), [], 'get_all_DBAdaptors() returns an array-ref even when the Registry is empty');
+
 my $multi_db = Bio::EnsEMBL::Test::MultiTestDB->new();
 my $db = $multi_db->get_DBAdaptor('core');
 my $dbc = $db->dbc();
 
-my $reg = 'Bio::EnsEMBL::Registry';
-
 my $registry_template = <<'TMPL';
 {
   package Reg;