Packer Plugin Installation Failure

### Version report

Jenkins and plugins versions report:

```
Jenkins version 2.302
Packer plugin 1.5
```

- What Operating System are you using (both controller, and any agents involved in the problem)?

```
CentOS 7
```

### Reproduction steps

Install packer plugin and then configure version in tools (Manage Jenkins > Global Tools Configuration)

### Results

Expected result:

Plugin should get installed.

Actual result:

```
packerInstallation:
installations: |-
FAILED TO EXPORT
biz.neustar.jenkins.plugins.packer.PackerInstallation$DescriptorImpl#installations: java.lang.IllegalArgumentException: argument type mismatch
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at io.jenkins.plugins.casc.impl.configurators.DataBoundConfigurator.describe(DataBoundConfigurator.java:308)
at io.jenkins.plugins.casc.Attribute._describe(Attribute.java:328)
at io.jenkins.plugins.casc.Attribute.describe(Attribute.java:257)
at io.jenkins.plugins.casc.Configurator.describe(Configurator.java:183)
at io.jenkins.plugins.casc.impl.configurators.GlobalConfigurationCategoryConfigurator.describe(GlobalConfigurationCategoryConfigurator.java:115)
at io.jenkins.plugins.casc.impl.configurators.GlobalConfigurationCategoryConfigurator.lambda$describe$3(GlobalConfigurationCategoryConfigurator.java:108)
at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175)
at java.util.Iterator.forEachRemaining(Iterator.java:116)
at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)
at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:485)
at io.jenkins.plugins.casc.impl.configurators.GlobalConfigurationCategoryConfigurator.describe(GlobalConfigurationCategoryConfigurator.java:108)
at io.jenkins.plugins.casc.impl.configurators.GlobalConfigurationCategoryConfigurator.describe(GlobalConfigurationCategoryConfigurator.java:33)
```

Start with PackerInstallation$DescriptorImpl#installations and the Global Tools Configuration path described in the issue. Reproduce the installation and version configuration on Jenkins 2.302 with Packer plugin 1.5, then inspect the reported DataBoundConfigurator argument-type mismatch. Done means the Packer plugin installs and its configured installation can be exported without the failure.

Written by the indexing model from the issue text.