Make Entity.getMut return non-nullable pointer

src/entity.zig

@@ -311,7 +311,7 @@ pub fn Entity(comptime ctx: anytype) type {
             return @alignCast(@ptrCast(ptr));
         }
 
-        pub fn getMut(self: Self, comptime T: type) ?*T {
+        pub fn getMut(self: Self, comptime T: type) *T {
             const id = Context.lookup(T).*;
             const ptr = c.ecs_get_mut_id(self.world.raw, self.raw, id);
             return @alignCast(@ptrCast(ptr));