Bug 123523 Previewing a scripted data set mapped to a java event handler throws NPE
When previewing a scripted data set we try to get a class loader from the ExecutionContext. (See ScriptExecutor.getClassUsingCustomClassPath). The context will be null in this case. The reason for using the context is to use cached class loaders when possible. Need to use some other mechanism to get the class loader if the context is null. We can either provide an external map to use as cache, or not bother with caching at all.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/script/element/IReportItem.java
* Sets the item's width to a value in default units. The default unit may
	 * be defined by the property in BIRT or the application unit defined in the
	 * design session.
	 * 
	 * @param dimension
	 *            the new value in application units.
	 * @throws ScriptException
	 *             if the property is locked.
	 */
	void setWidth( double dimension ) throws ScriptException;
	/**
	 * Gets a handle to deal with the item's width.
	 * 
	 * @return a DimensionHandle for the item's width.
	 */
	String getWidth( );
	/**
	 * Gets a handle to deal with the item's height.
	 * 
	 * @return a DimensionHandle for the item's height.
	 */
	String getHeight( );
	/**
	 * Returns the bookmark of the report item.
	 * 
	 * @return the book mark as a string
	 */
	String getBookmark( );
	/**
	 * Sets the bookmark of the report item.