The vibe I have gotten from talking to someone who would know is that the players like Lehner, he's a nice guy who tries hard, but he's a headcase and you kinda have to walk on egg shells around him so that he doesn't lose focus. As soon as he gets rattled he loses it. That's probably just who he is and unfortunately it is what is holding him back from being a truly great goalie. His mental game is poor. He's not a guy who thrives on pressure.
Ullmark, on the other hand, seems like the kind of guy who is unfazed by everything. He exudes positive vibes. He wont mope when he lets in a bad goal, and he wont make his teammates feel bad when they hang him out to dry. You'll probably never see a wtf wave from Ullmark.
I hope he keeps the Minions mask. That's his entire life attitude encapsulated in an object.