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
* 
	 * @param mode
	 *            presentation mode
	 */
	public void setPresentationMode( boolean mode )
	{
		this.presentationMode = mode;
	}
	/**
	 * get a string formatter object
	 * 
	 * @param value
	 *            string format
	 * @return formatter object
	 */
	public StringFormatter getStringFormatter( String value )
	{
		StringFormatter fmt = ( StringFormatter ) stringFormatters.get( value );
		if ( fmt == null )
		{
			fmt = new StringFormatter( value, locale );
			stringFormatters.put( value, fmt );
		}
		return fmt;
	}
	/**
	 * get a number formatter object
	 * 
	 * @param value
	 *            number format