'Codeunit "Temp Blob"' does not contain a definition for 'Blob'AL(AL0132)

Hi All,

I need to do some changes in standard report, 1305 - 'Standard Sales - Order Conf.'. For that I converted this report from CAL to AL. But I am getting some errors regarding TempBlob. I am able to resolved few errors by Googling. 

I am getting below error  on PreDataItem: 

'Codeunit "Temp Blob"' does not contain a definition for 'Blob'AL(AL0132)

Previously TempBlobWorkDescription was record, I changed it to codeunit.

Piece of code is as below,
trigger OnPreDataItem();
                    IF NOT ShowWorkDescription THEN
                    TempBlobWorkDescription.Blob := Header."Work Description";

I used https://github.com/microsoft/ALAppExtensions/blob/master/BREAKINGCHANGES.md link to resolve my errors. But not getting anything for above error. 
Could anyone suggest or help me how to resolve this error?
Thanks in advance.