Reference a a column for a list in Power Query

Dear All,

I have the following table:

Table1

Through the following step in PowerQuery:

= Table.TransformColumns( #"previous step", {{"CODE", (x)=> if x = null then List.Select(List.Distinct( #"previous step"[CODE]), each _<> null) else {x}}})

I achieve the following:

in column CODE, replace "null" with a list of all the distinct codes existent in column CODE except "null".

In this way, instead of nulls, I get a list of the following elements {724, 323, 455, 444, 256} 

Now, I have another table with a list of codes:

Table2

My question is: How do I reference CODE column in Table 2 in the previous step INSTEAD of CODE column in Table1?

Thank you for your time

gianmarco