NIFI-7805 ResultSetRecordSet can't generate a schema if first row con…

[patricker]

…tains NULL Decimal

Description of PR

When using ResultSetRecordSet, if the first row in a resultset contains a Decimal column with a NULL value, then NiFi fails to create a schema and throws an exception. This is because it is trying to read the Decimal Scale and Precision from the Decimal Value rather than from the Result Set Schema.

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[patricker]

@tpalfy @markap14 @simonbence
Small bug fix for #4223. If you have a minute to look it over I'd appreciate it.

[simonbence]

Good catch, LGTM

[pvillard31]

Thanks for the review @simonbence, it LGTM as well @patricker, merging, thank you.