Form1099-R , Box 2a is blank (for a Vanguard Roth IRA distribution--an account opened in 2016). I had a Roth IRA in 2012 which means I should not be taxed. What do I do?

The Roth IRA opened in 2012 was with American Funds.  I believe the rule is that if you had any Roth IRA older than 5 years, a distribution from any other Roth IRA will still qualify for no taxes due.  How do I enter this in Turbotax?