Bug 138562 Splite extendsexcpetion to seperate sub class
The suggestion is Parent invalid Cycle extends Different type extends Not top level extends
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/ExtendsCommand.java
|| DesignElement.USER_PROPERTIES_PROP.equals( propName ) )
					continue;
				Object localValue = element.getLocalProperty( module, propDefn );
				Object parentValue = parent.getStrategy( )
						.getPropertyFromElement( module, parent, propDefn );
				if ( localValue == null && parentValue != null )
				{
					PropertyCommand command = new PropertyCommand( module,
							element );
					if ( propDefn.getTypeCode( ) == PropertyType.STRUCT_TYPE )
					{
						command.makeLocalCompositeValue( new CachedMemberRef(
								propDefn ) );
					}
					else
					{
						command.setProperty( propDefn, ModelUtil.copyValue(
								propDefn, parentValue ) );
					}
				}
			}
			
			ExtendsCommand command = new ExtendsCommand( module, element );
			command.setExtendsElement( (DesignElement) null );
		}
		catch ( SemanticException ex )
		{
			activityStack.rollback( );
			throw ex;
		}