// Test case for issue #231

import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

public class SelfAssignment {

  void test(@Nullable String s) {
    assertNonNull(s);
    s = s.trim();
  }

  @EnsuresNonNull("#1")
  void assertNonNull(final @Nullable Object o) {
    if (o == null) {
      throw new AssertionError();
    }
  }
}