My goal is to import a generic JSON file that contains the result of a static analyzer tool that is not supported native.

As described in the documentation it should be able to use JSON log files with the Warnings Plugin: https://github.com/jenkinsci/warnings-ng-plugin/blob/master/doc/Documentation.md#export-your-issues-into-a-supported-format

From the documentation I expect that the following file would be parsed without problems: https://github.com/jenkinsci/warnings-ng-plugin/blob/master/src/test/resources/io/jenkins/plugins/analysis/warnings/json-issues.log

Creating a Jenkinsfile with the following content:
recordIssues( enabledForFailure: true, aggregatingResults: true, tools: [warningsPlugin()] )

Using this into the Jenkinsfile results in the following output:

Could not instantiate

for io.jenkins.plugins.analysis.core.steps.RecordIssuesStep: java.lang.UnsupportedOperationException: no known implementation of class io.jenkins.plugins.analysis.core.model.Tool is using symbol 'warningsPlugin'

So the bug is that I am unable to parse native JSON files as described in the documentation.