unable to specify MESH_ELASTICSEARCH_MAPPING_MODE

[mephinet]

I am unable to set the ElasticSearch Mapping Mode to strict via environment variables with Gentics Mesh 0.40.1:

$ docker run -e MESH_ELASTICSEARCH_MAPPING_MODE=STRICT -p 8080:8080  gentics/mesh-demo:0.40.1
...
13:17:26.181 [] INFO  [main] [c.g.m.e.c.env.Option] - Setting env via field access {MESH_ELASTICSEARCH_MAPPING_MODE=STRICT}
Exception in thread "main" java.lang.RuntimeException: Could no convert environment variable for type com.gentics.mesh.etc.config.search.MappingMode
        at com.gentics.mesh.etc.config.env.OptionUtils.convertValue(OptionUtils.java:45)
        at com.gentics.mesh.etc.config.env.OptionUtils.overrideWitEnvViaFieldSet(OptionUtils.java:85)
        at com.gentics.mesh.etc.config.env.Option.overrideWithEnv(Option.java:27)
        at com.gentics.mesh.etc.config.env.Option.overrideWithEnv(Option.java:40)
        at com.gentics.mesh.OptionsLoader.applyEnvironmentVariables(OptionsLoader.java:60)
        at com.gentics.mesh.OptionsLoader.createOrloadOptions(OptionsLoader.java:48)
        at com.gentics.mesh.demo.DemoRunner.main(DemoRunner.java:44)

From how I understand https://getmesh.io/docs/administration-guide/#_search_options , this is how it should be done...