Fix @Nonnull lies.

Change-Id: I32b4a4cd7828e8c3457072b897f5f2c3e0575ca3
Reviewed-on: http://gerrit.dmdirc.com/3790
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager

src/com/dmdirc/FrameContainer.java

@@ -62,7 +62,6 @@ import java.util.List;
 import java.util.Set;
 import java.util.concurrent.CopyOnWriteArrayList;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 import static com.google.common.base.Preconditions.checkState;
@@ -390,7 +389,7 @@ public abstract class FrameContainer {
      *
      * @return the associated connection, or {@code null}.
      */
-    @Nonnull
+    @Nullable
     public abstract Connection getConnection();
 
     /**