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