NullPointer exception while registering custom data table converter

Summary

NullPointer exception while registering custom data table converter

Current Behavior

Register the following table converter:

    @DataTableType
    public List convertDataTable(DataTable dataTable) {
        return new ArrayList();
    }

Define the following step:

    @Given("table {}=")
    public void setCustomDataTable(String name, List value) {
        log.debug("Param {} = {}", name, value);
    }

Create the following scenario:

Scenario: Compare empty data tables
    Given table empty_table=
      | test |
      |      |

Run the scenario:

Step failed
io.cucumber.core.exception.CucumberException: Could not convert arguments for step [table {}=] defined at 'com.cucumber.utils.context.stepdefs.ParamSteps.setCustomDataTable(java.lang.String,java.util.Map)'.
The details are in the stacktrace below.
	at io.cucumber.core.runner.PickleStepDefinitionMatch.couldNotConvertArguments(PickleStepDefinitionMatch.java:108)
	at io.cucumber.core.runner.PickleStepDefinitionMatch.runStep(PickleStepDefinitionMatch.java:52)
	at io.cucumber.core.runner.TestStep.executeStep(TestStep.java:64)
	at io.cucumber.core.runner.TestStep.run(TestStep.java:49)
	at io.cucumber.core.runner.PickleStepTestStep.run(PickleStepTestStep.java:46)
	at io.cucumber.core.runner.TestCase.run(TestCase.java:51)
	at io.cucumber.core.runner.Runner.runPickle(Runner.java:66)
	at io.cucumber.core.runtime.Runtime.lambda$null$2(Runtime.java:100)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at io.cucumber.core.runtime.Runtime$SameThreadExecutorService.execute(Runtime.java:243)
	at java.base/java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:118)
	at io.cucumber.core.runtime.Runtime.lambda$run$3(Runtime.java:100)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
	at java.base/java.util.stream.SliceOps$1$1.accept(SliceOps.java:199)
	at java.base/java.util.ArrayList$ArrayListSpliterator.tryAdvance(ArrayList.java:1631)
	at java.base/java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:127)
	at java.base/java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:502)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:488)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)
	at io.cucumber.core.runtime.Runtime.run(Runtime.java:101)
	at io.cucumber.core.cli.Main.run(Main.java:73)
	at io.cucumber.core.cli.Main.main(Main.java:31)
Caused by: io.cucumber.datatable.CucumberDataTableException: 'java.util.List' could not transform
      | test |
      |      |

	at io.cucumber.datatable.DataTableType.transform(DataTableType.java:124)
	at io.cucumber.datatable.DataTableTypeRegistryTableConverter.toListOrNull(DataTableTypeRegistryTableConverter.java:150)
	at io.cucumber.datatable.DataTableTypeRegistryTableConverter.convertEntryKeys(DataTableTypeRegistryTableConverter.java:262)
	at io.cucumber.datatable.DataTableTypeRegistryTableConverter.toMap(DataTableTypeRegistryTableConverter.java:216)
	at io.cucumber.datatable.DataTableTypeRegistryTableConverter.convert(DataTableTypeRegistryTableConverter.java:73)
	at io.cucumber.datatable.DataTable.convert(DataTable.java:357)
	at io.cucumber.core.stepexpression.StepExpressionFactory.lambda$createExpression$4(StepExpressionFactory.java:63)
	at io.cucumber.core.stepexpression.DataTableArgument.getValue(DataTableArgument.java:19)
	at io.cucumber.core.runner.PickleStepDefinitionMatch.runStep(PickleStepDefinitionMatch.java:47)
	... 24 more
Caused by: java.lang.NullPointerException
	at io.cucumber.java.AbstractDatatableElementTransformerDefinition.replaceEmptyPatternsWithEmptyString

[mpkorstanje]

Datatable.asMaps() has a value collision when null keys are used. Not actually an NPE but based on same assumption as the table entry NPE.

[fslev]

Actually, indeed I was doing something wrong. Inside my project I had some business code that was executing, and somewhere it threw a null pointer exception. Indeed, relevant stacktrace of my code was somehow swallowed.That’s why I first thought it was related to cucumber library. However, this issue is fixed.

Thanks for the replies.