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
* data engine, used to evaluate the data related expressions.
	 */
	private IDataEngine dataEngine;
	/**
	 * utility used to create the report content
	 */
	private ReportExecutor executor;
	/**
	 * utility used to create the TOC
	 */
	private TOCBuilder tocBuilder;
	
	/**
	 * report runnable used to create the report content
	 */
	private IReportRunnable runnable;
	/**
	 * the report design contained in the report runnable
	 */
	private Report report;
	/**
	 * Global configuration variables
	 */
	private Map configs = new BirtHashMap( );
	/**
	 * Report parameters used to create the report content
	 */
	private Map params = new BirtHashMap( );
	private Map persistentBeans = new HashMap( );
	private Map transientBeans = new HashMap( );