assertNullOrValidMapValue function
Assert that the value for key k in Map m is non-null and is of Type t. Throws an ArgumentError if the value is null, or is not of Type t.
Implementation
void assertNullOrValidMapValue(Map m, String k, Type t) {
var v = m[k];
if (v == null) {
return;
} else {
return assertValidMapValue(m, k, t);
}
}