Fix issues in validation.
Add integration tests for multiple name elements - create, update, delete.
Add integration tests for multiple structure elements - create, update, delete, approve, cancel, reject.

Declarations should use Java collection interfaces such as "List" rather than specific implementation classes such as "LinkedList"
Empty statements should be removed
JUnit assertTrue/assertFalse should be simplified to the corresponding dedicated assertion
JUnit5 test classes and methods should have default package visibility
Methods and field names should not be the same or differ only by capitalization
Nested "enum"s should not be declared static

Handle exceptions in service and controller layers.
Translate exceptions to http status codes in global exception handler.

Updated validation of mnemonic rules for structures and added docker integration tests for REST API endpoints for structures