Bug 165278 this.getDisplayContent()="" in script of text will destroy preview[0801]
Description: this.getDisplayContent()="" in script of text will destroy preview Build number:2.1.2.v20061120 and 2.2.0.v20061117 Steps to reproduce: 1. Insert a text item, select it and switch to script editor 2. Input this.getDisplayContent()="" and preview Expected result: Error message about the incorrect script. Actual result: In 2.1.2, I saw HTTP Status 500 - type Exception report message description The server encountered an internal error () that prevented it from fulfilling this request. In 2.2.0, I saw error dialog with java.lang.ClassCastException.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/executor/ExecutionContext.java
* 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;
	/**
	 * data engine, used to evaluate the data related expressions.
	 */
	private IDataEngine dataEngine;
	/**
	 * utility used to create the report content
	 */
	private IReportExecutor executor;
	/**
	 * utility used to create the TOC
	 */
	private TOCBuilder tocBuilder;
	
	/**
	 * report runnable used to create the report content
	 */
	private ReportRunnable runnable;
	/**
	 * Global configuration variables
	 */
	private Map configs = new BirtHashMap( );
	/**