[MC-97497] ClassCastException

Sorry, I don't really know what happened. I flied around in a singleplayer superflat world (around Y=65) and suddenly minecraft crashed. (I don't use mods.)
I got a ClassCastException, which means there's a bug in the code of class awj (name in 1.9-pre2) at one of these lines:

for(☃3 = 1; ☃3 <= 7; ++☃3) {
    ☃4 = ((akm)this.a).g(); // <-- This one
    int ☃5 = ☃4 / 3;
    this.a(☃, this.a.a(on.a(☃1, ☃5, ☃4)), 1, 1, ☃3, ☃2);
    this.a(☃, this.a.a(on.a(☃1, ☃5, ☃4)), 2, 1, ☃3, ☃2);
    int ☃6 = ((akm)this.b).g(); // <-- Or this one
    int ☃7 = ☃6 / 3;
    this.a(☃, this.b.a(on.a(☃1, ☃7, ☃6)), 4, 1, ☃3, ☃2);
    this.a(☃, this.b.a(on.a(☃1, ☃7, ☃6)), 5, 1, ☃3, ☃2);
}

See the attachment for the error I got.