Nullable type unnecessarily inferred converting List<? extends T> to List<? extends T>

More from playing around with #2719. This one is only a false positive and might well be a known issue. (I was going to say it could be part of #979, but javac 7 is able to infer that get(0) returns a String, so I would naively expect the Checker Framework to infer that it returns a non-null String.)

import static java.util.Arrays.asList;

import java.util.List;

class Foo {
  void foo() {
    passThrough(asList("x")).get(0).length();
  }

  <T> List<? extends T> passThrough(List<? extends T> object) {
    return object;
  }
}

$ checker/bin/javac -processor org.checkerframework.checker.nullness.NullnessChecker Foo.java 
Foo.java:7: error: [dereference.of.nullable] dereference of possibly-null reference passThrough(asList("x")).get(0)
    passThrough(asList("x")).get(0).length();
                                ^
1 error

Interestingly, if I change foo() to the following, then it compiles:

  String foo() {
    return passThrough(asList("x")).get(0);
  }

And of course it also compiles if I pass an explicit <String> argument to either asList or passThrough.