Bug 163018 An error extension will lead the report contain chart can't be opened and can not new a report.
Details: An error extension will lead the report contain chart can't open In org.eclipse.birt.report.tests.model has an error extension. When run the birt use workbenck, the report contain chart can't be opened and it can not new a report.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/metadata/ElementDefn.java
* should not be added/removed. Otherwise, cachedProperties can be
	 * un-synchronized.
	 */
	protected Map cachedProperties = new LinkedHashMap( );
	/**
	 * Sets the Java class which implements this element.
	 * 
	 * @param theClass
	 *            the Java class to set
	 */
	void setJavaClass( String theClass )
	{
		assert !isBuilt;
		javaClass = theClass;
	}
	/**
	 * Sets the name of the style which "selects" this element.
	 * 
	 * @param value
	 *            The predefined style name.
	 */
	void setSelector( String value )
	{
		selector = value;
	}
	/**
	 * Sets the "extends" attribute.
	 * 
	 * @param base
	 *            The name of the element type which this element extends.