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/executor/ExecutionContext.java
{
	
	private static Logger log = Logger.getLogger( ExecutionContext.class
			.getName( ) );
	
	public static final String PROPERTYSEPARATOR = ";";
	
	
	private ReportEngine engine;
	/**
	 * task ID string
	 */
	private String taskIDString;
	/**
	 * execution mode, in this mode, the render operation should be executed.
	 */
	private boolean presentationMode = false;
	/**
	 * execution mode, in this mode, the genreation opration should be executed.
	 */
	private boolean factoryMode = true;
	
	/**
	 * The scripting context, used to evaluate the script.
	 */
	private ScriptContext scriptContext;
	/**