Add nullity check before fetching value from JPA repository

[chriskormaris]

https://github.com/aileftech/snap-admin/blob/297224dafe486cb45666c4a33907ea1f4c94bc2d/src/main/java/tech/ailef/snapadmin/external/dbmapping/CustomJpaRepository.java#L147C1-L148C1

Please change above line to this:

if (field.getConnectedSchema() != null && value != null)