[Bug]: DefaultMigrationService uses assert instead of exceptions for validation

[Splatcrafter]

AI REVIEWED

Module: spring-boot-starter
File: spring/service/DefaultMigrationService.java (~line 413-414)
Severity: High

Summary

Builder validation uses assert statements which are disabled by default in production JVMs:

assert from != null : "fromVersion must be set";
assert to != null : "toVersion must be set";

Expected Behavior

Validation should always execute, throwing IllegalStateException for invalid builder state.

Actual Behavior

With -ea disabled (production default), invalid builder states pass silently to the migration call, causing confusing NPEs later.

Suggested Fix

if (from == null) throw new IllegalStateException("fromVersion must be set");
if (to == null) throw new IllegalStateException("toVersion must be set");