Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/DataSetParameterHandle.java
*/
	public String getDefaultValue( )
	{
		return (String) getProperty( DataSetParameter.DEFAULT_VALUE_MEMBER );
	}
	/**
	 * Checks whether this parameter is an input parameter.
	 * 
	 * @return <code>true</code> if it is an input parameter. Otherwise
	 *         <code>false</code>.
	 */
	public boolean isInput( )
	{
		return ( (Boolean) getProperty( DataSetParameter.IS_INPUT_MEMBER ) )
				.booleanValue( );
	}
	/**
	 * Sets whether this parameter is an input parameter.
	 * 
	 * @param isInput
	 *            <code>true</code> if it is an input parameter. Otherwise
	 *            <code>false</code>.
	 */
	public void setIsInput( boolean isInput )
	{
		setPropertySilently( DataSetParameter.IS_INPUT_MEMBER, Boolean
				.valueOf( isInput ) );
	}
	/**
	 * Checks whether the value of this parameter can be <code>null</code>.