Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/JoinConditionHandle.java
* Sets the right data set value of this condition.
	 * 
	 * @param rightDataset
	 *            the right data set to set
	 */
	public void setRightDataSet( String rightDataset )
	{
		setPropertySilently( JoinCondition.RIGHT_DATASET_MEMBER, rightDataset );
	}
	/**
	 * Returns right data set value this condition.
	 * 
	 * @return the right data set value
	 */
	public String getRightDataSet( )
	{
		return getStringProperty( JoinCondition.RIGHT_DATASET_MEMBER );
	}
	/**
	 * Sets the left expression value of this condition.
	 * 
	 * @param leftExpression
	 *            the left expression to set
	 */
	public void setLeftExpression( String leftExpression )
	{
		setPropertySilently( JoinCondition.LEFT_EXPRESSION_MEMBER,
				leftExpression );
	}
	/**