Named constants are (usually) not null.

lib/src/compiler/nullable_type_inference.dart

Index: lib/src/compiler/nullable_type_inference.dart
diff --git a/lib/src/compiler/nullable_type_inference.dart b/lib/src/compiler/nullable_type_inference.dart
index 0cbfd4ccd728cd30ee3841a696b6c834a9617331..706d677eacab6bb697116d0505632408544eb2fb 100644
--- a/lib/src/compiler/nullable_type_inference.dart
+++ b/lib/src/compiler/nullable_type_inference.dart
@@ -78,6 +78,11 @@ abstract class NullableTypeInference {
         return false;
       }
 
+      if (element is PropertyAccessorElement && element.isGetter) {
+        PropertyInducingElement variable = element.variable;
+        return variable.constantValue?.isNull ?? true;
+      }
+
       // Other types of identifiers are nullable (parameters, fields).
       return true;
     }