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...)
Mario de Sousa <msousa@fe.up.pt> [Wed, 13 Feb 2019 14:16:26 +0000] rev 1086
merge
Mario de Sousa <msousa@fe.up.pt> [Wed, 26 Dec 2018 19:36:03 +0000] rev 1085
fix issue #73: add missing overloaded functions ADD, SUB, MUL and DIV for TIME, TOD, DT, ...