New Zealand opener Martin Guptill has been released from his national contract after being omitted from the squad for the India T20 series, heralding the end of the veteran batsman's international career.New Zealand's top run-scorer in T20 and third-highest in one day cricket, 36-year-old Guptill has been out of favour with selectors who opted for rising star Finn Allen against India and at the recent World Cup in Australia.Guptill said he would still make himself available for New Zealand selection but was "realistic enough" to understand the need to consider his playing options."I’m still available for New Zealand, I have the chance to explore other opportunities and I also get to spend more time with my family – which is important,” he said in a New Zealand Cricket (NZC) statement on Wednesday.NZC said it made it clear to Guptill that preference in selections would continue to be given to players with national or domestic contracts.Guptill is the third Black Caps player to ask for a release from his contract in recent months, with fast bowling team mate Trent Boult and all-rounder Colin de Grandhomme also opting to pursue other opportunities.NZC boss David White said he was comfortable with the existing contract and selection system."We understand Martin’s position," White said."Martin's been a giant of the white ball game, a committed and well-respected member of the Black Caps, and has earned the right to play out his career on his own terms."