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
/**
	 * create a new context. Call close to finish using the execution context
	 */
	public ExecutionContext( int taskID )
	{
		this( null, taskID );
	}
	/**
	 * create a new context. Call close to finish using the execution context
	 */
	public ExecutionContext( IReportEngine engine, int taskID )
	{
		this.engine = engine;
		taskIDString = "Task" + new Integer( taskID ).toString( ); 
		locale = Locale.getDefault( );
		ScriptableObject rootScope = null;
		if ( engine != null )
		{
			Object scope = engine.getRootScope( );
			if ( scope instanceof ScriptableObject )
			{
				rootScope = (ScriptableObject) scope;
			}
		}
		if ( rootScope != null )
		{
			scriptContext = new ScriptContext( rootScope );
		}
		else
		{