All types are non-nullable

Nil, the null type of Cyan, can only be assigned to variables of type Dyn, Nil, or a union that has the Nil type. See the example:

var String s;
s = "abc"; 
s = Nil; // compilation error
var String|Nil sn;
sn = "Cyan"; 
sn = Nil; // ok
var Nil|String|Int|Char ns;
ns = 0;
ns = "Cyan";
ns = 'a';
ns = Nil; // ok
var Dyn d;
d = 0;
d = "Cyan";
d = Nil; // ok

If Dyn is not used, there will never be a runtime error caused by Nil.