Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/FilterConditionHandle.java
* <li><code>FILTER_TARGET_DATA_SET</code>
	 * <li><code>FILTER_TARGET_RESULT_SET</code>
	 * </ul>
	 * 
	 * @return the target type
	 */
	public String getFilterTarget( )
	{
		return (String) getProperty( FilterCondition.FILTER_TARGET_MEMBER );
	}
	/**
	 * Sets the filter target. The allowed values are defined in
	 * {@link org.eclipse.birt.report.model.api.elements.DesignChoiceConstants},
	 * and they are:
	 * <ul>
	 * <li><code>FILTER_TARGET_DATA_SET</code>
	 * <li><code>FILTER_TARGET_RESULT_SET</code>
	 * </ul>
	 * 
	 * @param filterTarget
	 *            the filter target to set
	 * 
	 * @throws SemanticException
	 *             if the value is not one of the above.
	 */
	public void setFilterTarget( String filterTarget ) throws SemanticException
	{
		setProperty( FilterCondition.FILTER_TARGET_MEMBER, filterTarget );
	}
}