I have a table with 1m records, with 100k records having null on `colA`. Remaining records have pretty distinct values, is there a difference in creating a regular index on this column vs a partial index with `where colA is not null`?

Since regular Postgres indexes do not store NULL values, wouldn't it be the same as creating a partial index with `where colA is not null`?  

Any pros or cons with either indexes?