transitServiceEnd and transitServiceStart cannot be '' despite docs

[dzfranklin]

Expected behavior

If transitServiceStart and transitServiceEnd are specified as '' the period will be unbounded, as documented

Observed behavior

17:29:24.792 ERROR [main]  (OTPMain.java:57) The parameter value '' is not a Period or LocalDate. Details: Text '' could not be parsed at index 0 Parameter: transitServiceStart. Source: build-config.json.
org.opentripplanner.framework.application.OtpAppException: The parameter value '' is not a Period or LocalDate. Details: Text '' could not be parsed at index 0 Parameter: transitServiceStart. Source: build-config.json.
        at org.opentripplanner.standalone.config.framework.json.NodeAdapter.createException(NodeAdapter.java:302)
        at org.opentripplanner.standalone.config.framework.json.NodeAdapter.createException(NodeAdapter.java:311)
        at org.opentripplanner.standalone.config.framework.json.ParameterBuilder.error(ParameterBuilder.java:742)
        at org.opentripplanner.standalone.config.framework.json.ParameterBuilder.parseRelativeLocalDate(ParameterBuilder.java:678)
        at org.opentripplanner.standalone.config.framework.json.ParameterBuilder.lambda$asDateOrRelativePeriod$4(ParameterBuilder.java:386)
        at org.opentripplanner.standalone.config.framework.json.ParameterBuilder.ofOptionalString(ParameterBuilder.java:519)
        at org.opentripplanner.standalone.config.framework.json.ParameterBuilder.asDateOrRelativePeriod(ParameterBuilder.java:386)
        at org.opentripplanner.standalone.config.BuildConfig.<init>(BuildConfig.java:407)
        at org.opentripplanner.standalone.config.BuildConfig.<init>(BuildConfig.java:198)
        at org.opentripplanner.standalone.config.OtpConfigLoader.loadBuildConfig(OtpConfigLoader.java:93)
        at org.opentripplanner.standalone.config.ConfigModel.<init>(ConfigModel.java:71)
        at org.opentripplanner.standalone.config.configure.LoadConfigModule.providesModel(LoadConfigModule.java:39)
        at org.opentripplanner.standalone.config.configure.LoadConfigModule_ProvidesModelFactory.providesModel(LoadConfigModule_ProvidesModelFactory.java:47)
        at org.opentripplanner.standalone.config.configure.LoadConfigModule_ProvidesModelFactory.get(LoadConfigModule_ProvidesModelFactory.java:38)
        at org.opentripplanner.standalone.config.configure.LoadConfigModule_ProvidesModelFactory.get(LoadConfigModule_ProvidesModelFactory.java:13)
        at dagger.internal.DoubleCheck.getSynchronized(DoubleCheck.java:54)
        at dagger.internal.DoubleCheck.get(DoubleCheck.java:45)
        at org.opentripplanner.standalone.configure.DaggerLoadApplicationFactory$LoadApplicationFactoryImpl.configModel(DaggerLoadApplicationFactory.java:166)
        at org.opentripplanner.standalone.configure.LoadApplication.config(LoadApplication.java:96)
        at org.opentripplanner.standalone.OTPMain.startOTPServer(OTPMain.java:114)
        at org.opentripplanner.standalone.OTPMain.main(OTPMain.java:55)

Version of OTP used (exact commit hash or JAR name)

otp-shaded-2.8.1.jar

Data sets in use (links to GTFS and OSM PBF files)

N/A

Command line used to start OTP

java -Xmx8G -jar "$OTP" --loadStreet --save --cache ./otp/cache ./otp

Router config and graph build config JSON

build_config.json

{
  "streetGraph": "streetGraph.obj",
  "writeCachedElevations": true,
  "transitServiceStart": "",
  "transitServiceEnd": "",
  "osmDefaults": {
    "timeZone": "Europe/London",
    "osmTagMapping": "uk"
  },
  "transferRequests": [
    {
      "modes": "WALK"
    }
  ]
}

router_config.json

{
  "routingDefaults": {
    "drivingDirection": "left",
    "transferOptimization": {
      "optimizeTransferWaitTime": false // workaround for crash on some rail transfers
    }
  },
  "transit": {
    "dynamicSearchWindow": {
      "maxWindow": "PT24H"
    }
  }
}

Steps to reproduce the problem

Just build with that build config