Dealing with nulls when checking email format in a new column

Hi

I have a column of emails (called 'Main Email Address'). I have an add column step that works well to check the email addresses for any that do not look like email addresses and if so it just adds a null for them.

= Table.AddColumn(#"Replaced Value1", "Custom", each if Text.Contains([Main Email Address], "@") and Text.Contains(Text.Range([Main Email Address], Text.PositionOf([Main Email Address], "@")), ".") then [Main Email Address] else null)

The problem is that the initial column ('Main Email Address') also contains nulls which is fine I would like to keep these in the new 'Custom' column however the code above produces an error (see below) every time it tries to run on a null email address (I think its to do with text.contains not being exectuable perhaps on a null value). Can anyone suggest what syntax I need to fix this?

Example Input and Output required:

Main Email Address (type text)      Custom (type text)

null                                                  null

null                                                  null

[email protected]                        [email protected]

[email protected]                       [email protected]

No Email Address                            null

NoEmail                                           null

[email protected]                       [email protected]

null                                                  null

01234567                                        null

[email protected]                       [email protected] 

Thanks for any help. I am sure its something simple I need to add. My first attempt to post this got flagged as spam so trying using code around the emails!