Returns one loan file, with each block nested inside it. Sensitive
fields come back masked. You'll get a 404 if the loan is not on
your processing company's account.

Every field is always there. When a field has no value you get
an explicit null — so the shape of the reply never changes from
one loan to the next. That matches PATCH, where sending null is
how you clear a field.

A field reads as null in any of these cases: nothing was ever
entered; the stored text is not a number but the field is numeric,
such as N/A, which is reported as null rather than invented as
0; or the stored value is 0 on one of the loan-terms money and
rate fields, or on loanLienPosition or propertyType, where a
genuine zero and "never entered" cannot be told apart. The back
office shows both as blank, and this API matches it. The useful
consequence: when a field is not null, the value in it is real.