Handle null library in _NameTypeChecker.

Author: davidmorgan

source_gen/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 4.0.2-wip
+
+- Bug fix: fix possible null pointer exception in `TypeChecker.typeNamed` on
+  invalid code.
+
 ## 4.0.1
 
 - Require `analyzer: '>=8.1.1 <9.0.0'`.

source_gen/lib/src/type_checker.dart

@@ -257,7 +257,9 @@ class _NameTypeChecker extends TypeChecker {
 
   @override
   bool isExactly(Element element) {
-    final uri = element.library!.uri;
+    final library = element.library;
+    if (library == null) return false;
+    final uri = library.uri;
     return element.name == _typeName &&
         (_inPackage == null ||
             (((uri.scheme == 'dart') == _inSdk) &&