Dart produces compile error whereas analyzer does not when trying to add null to null.

[iarkh]

Dart version: 2.2.1-dev.1.1
OS: Windows 10

The following test example tries to calculate null + null expression:

main() {
	try { null + null;} catch (e) {}
	print("OK");
}

Analyzer passes with this whereas dart unexpectedly produces compile time error.

Sample output is:

$> dartanalyzer test.dart
Analyzing test.dart...
No issues found!
$>
$> dart test.dart
test.dart:2:13: Error: The method '+' isn't defined for the class 'Null'.
Try correcting the name to the name of an existing method, or defining a method named '+'.
try { null + null;} catch (e) {}
$>

Please note if I change the source for the following:

main() {
	try { 1 + null;} catch (e) {}
	print("OK");
}

it works as expected: dart throws runtime exception, and so finally it prints "OK" as expected.

[iarkh]

One more failing example:

main() {
	try {null >> 1;} catch (e) {}
	print("OK");
}

[lrhn]

The CFE is correct and the analyzer is wrong. The error is not entirely unexpected.

We changed the static type of null to be Null as part of the Dart 2 changes, rather than bottom as part of the preparation for Dart 2 (CL). This was to prevent the bottom type from being propagated around by type inference (a List<bottom> is a curious beast). We also changed Null to be a proper sub-type of every other type. With non-nullable types, that too will cease to be the case.

A consequence of that is that null + anything is a static type error because null does not have any + method.

The 1 + null succeeds because Null is a subtype of num, so it is a valid argument to int.operator+—which then fails at runtime because int.operator+ doesn't accept null arguments.

[eernstg]

Note #27273 and #36113 about missing errors from the analyzer about null and Null.

[srawlins]

Not sure when this was fixed, but Dart analyzer 2.5.0 now produces the following warning:

The operator '+' isn't defined for the class 'Null'.