How to expand record without mostly null values

Maybe try

Table.TransformColumns(Source, {"parameters", Record.Combine})

On the step when parameters is still a list.  This will provide cleaner expansion if each record does not have fields with null values.  I am hoping the nulls just come because you have a bunch of different records with different field names and when expanding the records at the same time you get nulls because the fields don't exist in other records.  When you click on an invidual cell you can see what the record looks like below.

If records that are being combined have the same field, it will be overwritten by the latest value.

Combining [A = 1]  with [A = null, B = 2] will give you [A = null, B = 2].

Combining [A = 1] with [B = 2] will give you [A = 1, B = 2].