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
* 
	 * @param value
	 *            the property value to be set.
	 * @throws ScriptException
	 *             if the property is locked.
	 */
	void setBookmark( String value ) throws ScriptException;
	/**
	 * Sets a table of contents entry for this item. The TOC property defines an
	 * expression that returns a string that is to appear in the Table of
	 * Contents for this item or its container.
	 * 
	 * @param expression
	 *            the expression that returns a string
	 * @throws ScriptException
	 *             if the TOC property is locked by the property mask.
	 * 
	 * @see #getTocExpression()
	 */
	void setTocExpression( String expression ) throws ScriptException;
	/**
	 * Returns the expression evalueated as a table of contents entry for this
	 * item.
	 * 
	 * @return the expression evaluated as a table of contents entry for this
	 *         item
	 * @see #setTocExpression(String)
	 */
	String getTocExpression( );
}