PURL Format Discrepancy

### Current Behavior


Although, The Purl format on [Dependency Track](https://docs.dependencytrack.org/datasources/routing/) and [Purl-Spec](https://github.com/package-url/purl-spec) mentions that `Namespace/GroupID` is optional.

For JAVA (Maven) packages, Dependency Track fails to find vulnerabilities in the Java Maven SBOM If `Namespace/GroupID` is not mentioned in the Purl.

### Proposed Behavior

scheme:type/namespace/name@version

** Namespace is not optional, IT IS a MUST in the Purl-Spec format for a `JAVA - Maven `SBOM for being detectable by Dependency Track.

### Checklist

- [X] I have read and understand the [contributing guidelines](https://github.com/DependencyTrack/dependency-track/blob/master/CONTRIBUTING.md#filing-issues)
- [X] I have checked the [existing issues](https://github.com/DependencyTrack/dependency-track/issues) for whether this enhancement was already requested

Start by reading the linked Dependency-Track routing documentation and the PURL specification, then reproduce the failure with a Java Maven SBOM whose PURL omits the namespace or GroupID. Trace how that component is processed for vulnerability lookup. Done means the documented optional-namespace case is handled consistently and vulnerability detection is verified for the affected SBOM.

Written by the indexing model from the issue text.