[MPIR-397] dependency-management report fails on managed dependencies with 'null' version

**[Carsten Rohde](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=carsten.rohde@obi.de)** opened **[MPIR-397](https://issues.apache.org/jira/browse/MPIR-397?redirect=false)** and commented

Maven allows to have managed dependencies without a version. This can be very useful, because this way you can change the scope of a transitive dependency without affecting the resolved version.

The dependency-management report however fails under such circumstances:

```java
Error generating maven-project-info-reports-plugin:3.1.0:dependency-management report: For artifact {pirbugdemo:pirbug-transitive:null:jar}: The version cannot be empty
```

There has been a similar issue with the versions-maven-plugin: https://github.com/mojohaus/versions-maven-plugin/issues/114

The example mainly consists of a "consumer" module with a dependency to a "dependency" module wich in turn has a dependency to a third module "transitive". In the consumer module, the "transitive" dependency is managed without setting the version.

If there is a workaround, please let me know.

Thanks a lot!

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**Affects:** 2.7, 2.9, 3.0.0, 3.1.0

**Attachments:**
- [pirbug-aggregator.zip](https://issues.apache.org/jira/secure/attachment/13007722/pirbug-aggregator.zip) (_7.81 kB_)

Start with the attached pirbug-aggregator.zip reproducer and run the dependency-management report on its consumer module, where the transitive dependency is managed without a version. Trace the report generation until the null-version artifact fails; done means the report completes and represents the managed dependency without raising “The version cannot be empty”.

Written by the indexing model from the issue text.