Consider this code:
---
public class Test {
     private void test() {
         Undefined x = Undefined.create();
     }
}
---

When compiled, this code produces the following errors:
---
Test.java:3: error: cannot find symbol
         Undefined x = Undefined.create();
         ^
  symbol: class Undefined
  location: class Test
Test.java:3: error: cannot find symbol
         Undefined x = Undefined.create();
                       ^
  symbol: variable Undefined
  location: class Test
2 errors
---

The latter error may be confusing, as the unresolvable "Undefined" identifier may also (more likely in this case) refer to an unknown class.

Original report:
http://mail.openjdk.java.net/pipermail/compiler-dev/2015-April/009399.html