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/ExtensionLoader.java
* @throws ExtensionException
		 *             if the value is empty
		 */
		void checkRequiredAttribute( String name, String value )
				throws ExtensionException
		{
			if ( StringUtil.isBlank( value ) )
				throw new ExtensionException( new String[]{name},
						ExtensionException.DESIGN_EXCEPTION_VALUE_REQUIRED );
		}
		/**
		 * Loads one choice.
		 * 
		 * @param choiceTag
		 *            the choice tag
		 * @param choice
		 *            the extension choice set load
		 * @param propDefn
		 *            the property definition in which the choices are inserted
		 * @throws ExtensionException
		 *             if the class some attribute specifies can not be
		 *             instanced.
		 */
		void loadChoice( IConfigurationElement choiceTag,
				ExtensionChoice choice, PropertyDefn propDefn )
				throws ExtensionException
		{
			
			String name = choiceTag.getAttribute( NAME_ATTRIB );
			checkRequiredAttribute( NAME_ATTRIB, name );