Bug 232777 [Viewers] ViewerDropAdapter holds currentTarget forever
Build ID: 3.3.2 Member currentTarget should be set to null after drop or after cancel, because it holds a domain object, which can't be garbage collected after Viewer.setInput(null).
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerDropAdapter.java
private Object currentTarget;
    /**
     * Information about the position of the mouse relative to the
     * target (before, on, or after the target.  Location is one of
     * the <code>LOCATION_* </code> constants defined in this type.
     */
    private int currentLocation;
    /**
     * A flag that allows adapter users to turn the insertion
     * feedback on or off. Default is <code>true</code>.
     */
    private boolean feedbackEnabled = true;
    /**
     * A flag that allows adapter users to turn auto scrolling
     * on or off. Default is <code>true</code>.
     */
    private boolean scrollEnabled = true;
    /**
     * A flag that allows adapter users to turn auto
     * expanding on or off. Default is <code>true</code>.
     */
    private boolean expandEnabled = true;
    
    /**
     * A flag that allows adapter users to turn selection feedback
     *  on or off. Default is <code>true</code>.
     */
    private boolean selectFeedbackEnabled = true;
    /**
     * Creates a new drop adapter for the given viewer.