Bug 124620 Referenced Parameter icon should be invalid if the parameter in library is deleted
Description: Referenced parameter icon should be invalid if the source parameter in library is deleted. Steps to reproduce: 1.Create a library. Insert a report scalar parameter. 2.Create a report, use the above library. In the library explorer, pull the parameter to the data explorer view of report. 3.Open the library file, delete the parameter. Then reopen the report design file, the icon of parameter seems nothing happened. But if those operations happened in dataset, the icon of dataset in the report will be invalid. It is acceptable. Expected Result: The icon of referenced parameter should be invalid.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
return null;
		if ( value instanceof BigDecimal )
			return (BigDecimal) value;
		ElementPropertyDefn prop = getPropertyDefn( propName );
		PropertyType type = MetaDataDictionary.getInstance( ).getPropertyType(
				prop.getTypeCode( ) );
		return type.toNumber( module, value );
	}
	/**
	 * Applies a design visitor. The derived element calls the corresponding
	 * visitMumble( ) method in the visitor. The visitor allows an algorithm to
	 * be implemented in a single visitor class, rather than all across the
	 * element inheritance hierarchy.
	 * 
	 * @param visitor
	 *            The visitor to apply.
	 */
	public abstract void apply( ElementVisitor visitor );
	/**
	 * Gets a property converted to a string value.
	 * 
	 * @param module
	 *            the module
	 * @param propName
	 *            The name of the property to get.
	 * @return The property value as a string.
	 */
	public String getStringProperty( Module module, String propName )
	{
		ElementPropertyDefn prop = getPropertyDefn( propName );