Fix #10425 - Value of "currency_id" in custom table changes from NULL to an empty string when saving

[serhiisamko091184]

Description

See the issue:
#10425

Motivation and Context

How To Test This

See the issue:
#10425

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Final checklist

• My code follows the code style of this project found here.
• My change requires a change to the documentation.
• I have read the How to Contribute guidelines.

[gunnicom]

I would fix that globally by changing one line in D manager.php. I do not have my fix at hand because I am on vacation right now.
I think it is just adding a && strlen($data[$field])>0) to this line

SuiteCRM/include/database/DBManager.php

Line 546 in 1a114a9

if (isset($data[$field])) {

Works for me since years and solves additional problems if for example you really need a unique column and so define it in the database table.
Already commented that on #9524
But of course we can make code more complicated by just doing more ifs for each data type.