Wed, 13 Feb 2019 14:40:26 +0000add default NULL value to references (as suggested by anonymous in issue 62)
Mario de Sousa <msousa@fe.up.pt> [Wed, 13 Feb 2019 14:40:26 +0000] rev 1087
add default NULL value to references (as suggested by anonymous in issue 62)
(Not really needed, but it is good practise...)

Wed, 13 Feb 2019 14:16:26 +0000merge
Mario de Sousa <msousa@fe.up.pt> [Wed, 13 Feb 2019 14:16:26 +0000] rev 1086
merge