Bug 122850 Table/list should not be able to be inserted in Master Page mode.
Description: Table/list should not be able to be inserted in Master Page mode. Steps to reproduce: 1. New a report and transfer to Master Page mode. 2. New a datasource and dataset 3. Drag a list/table to page header/footer, bind it to dataset and drag some columns inside. 4. Save and preview Expected result: Insert list/table item in master page should be forbidden. Actual result: They are allowed and preview showed "undefine" in page
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
return new ArrayList( derived );
		return new ArrayList( );
	}
	/**
	 * Returns the valid status of this element. Child elements need to
	 * overwrite this method to say in which condition they can be said valid or
	 * not.
	 * <p>
	 * for example, if a JDBCDataSource can not reach the server, then it's
	 * invalid.
	 * <p>
	 * UI needs this method to show different icon for each element in the user
	 * interface.
	 * 
	 * @return true if this element is valid, false otherwise.
	 */
	public boolean isValid( )
	{
		return isValid;
	}
	/**
	 * Sets whether the element is valid.
	 * 
	 * @param isValid
	 *            the valid to set
	 */
	public void setValid( boolean isValid )
	{
		this.isValid = isValid;
	}