Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/DataSetParameterHandle.java
* 
	 * @return <code>true</code> if the value can be <code>null</code>.
	 *         Otherwise <code>false</code>.
	 * @deprecated Use <code>allowNull()</code>
	 */
	public boolean isNullable( )
	{
		return allowNull( );
	}
	/**
	 * Sets whether the value of this parameter can be <code>null</code>.
	 * 
	 * @param isNullable
	 *            <code>true</code> if the value can be <code>null</code>.
	 *            Otherwise <code>false</code>.
	 * @deprecated Use <code>setAllowNull(boolean)</code>
	 */
	public void setIsNullable( boolean isNullable )
	{
		setAllowNull( isNullable );
	}
	/**
	 * Checks whether the value of this parameter can be <code>null</code>.
	 * 
	 * @return <code>true</code> if the value can be <code>null</code>.
	 *         Otherwise <code>false</code>.
	 */
	public boolean allowNull( )
	{
		return ( (Boolean) getProperty( DataSetParameter.ALLOW_NULL_MEMBER ) )