get_all_DBEntries should return [] instead of undef if there are no xrefs

modules/Bio/EnsEMBL/Gene.pm

@@ -519,6 +519,8 @@ sub get_all_DBEntries {
       $self->adaptor->db->get_DBEntryAdaptor->fetch_all_by_Gene($self);
   }
 
+  $self->{'dbentries'} ||= [];
+
   return $self->{'dbentries'};
 }
 

modules/Bio/EnsEMBL/Transcript.pm

@@ -134,6 +134,8 @@ sub get_all_DBEntries {
       $self->adaptor->db->get_DBEntryAdaptor->fetch_all_by_Transcript($self);
   }
 
+  $self->{'dbentries'} ||= [];
+
   return $self->{'dbentries'};
 }
 

modules/Bio/EnsEMBL/Translation.pm

@@ -354,6 +354,8 @@ sub get_all_DBEntries {
       $self->adaptor->db->get_DBEntryAdaptor->fetch_all_by_Translation($self);
   }
 
+  $self->{'dbentries'} ||= [];
+
   return $self->{'dbentries'};
 }