Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/JoinConditionHandle.java
}
	/**
	 * Returns operator value this condition.
	 * 
	 * @return the operator value
	 */
	public String getOperator( )
	{
		return getStringProperty( JoinCondition.JOIN_OPERATOR_MEMBER );
	}
	/**
	 * Sets the left data set value of this condition.
	 * 
	 * @param leftDataset
	 *            the left data set to set
	 */
	public void setLeftDataSet( String leftDataset )
	{
		setPropertySilently( JoinCondition.LEFT_DATASET_MEMBER, leftDataset );
	}
	/**
	 * Returns left data set value this condition.
	 * 
	 * @return the left data set value
	 */
	public String getLeftDataSet( )
	{
		return getStringProperty( JoinCondition.LEFT_DATASET_MEMBER );
	}
	/**