NullPointerException in Stream

Just a small blurb. I recently helped a colleague who got a NullPointerException whilst dealing with streams.

It looked very innocuous at first.

  @Test(expectedExceptions = NullPointerException.class)
  public void testStream() {
    Optional<String> first = Stream.of(new Person(null, "mrBear"), new Person("George", "Boole"),
            new Person("Ada", "Lovelace"),
            new Person("Tim", "Berners-Lee"), new Person("James", "Gosling"), new Person("Linus", "Torvalds"))
        .map(Person::firstName).findFirst();
  }

Well, it turns out that, if you have a list with null-values, and you try a findFirst() on the stream, and the first value is null, Java will attempt to wrap the null-value into an Optional, which is not allowed.

You get a fancy stacktrace, that shows just this:

java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:208)
	at java.base/java.util.Optional.of(Optional.java:113)
	at java.base/java.util.stream.FindOps$FindSink$OfRef.get(FindOps.java:194)
	at java.base/java.util.stream.FindOps$FindSink$OfRef.get(FindOps.java:191)
	at java.base/java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:150)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:647)
	at com.mrbear.streams.NullPointerExceptionTest.testStream(NullPointerExceptionTest.java:18)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:124)
	at org.testng.internal.Invoker.invokeMethod(Invoker.java:571)
	at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:707)
	at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:979)
	at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:125)
	at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:109)
	at org.testng.TestRunner.privateRun(TestRunner.java:648)
	at org.testng.TestRunner.run(TestRunner.java:505)
	at org.testng.SuiteRunner.runTest(SuiteRunner.java:455)
	at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:450)
	at org.testng.SuiteRunner.privateRun(SuiteRunner.java:415)
	at org.testng.SuiteRunner.run(SuiteRunner.java:364)
	at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
	at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:84)
	at org.testng.TestNG.runSuitesSequentially(TestNG.java:1187)
	at org.testng.TestNG.runSuitesLocally(TestNG.java:1116)
	at org.testng.TestNG.runSuites(TestNG.java:1028)
	at org.testng.TestNG.run(TestNG.java:996)
	at com.intellij.rt.testng.IDEARemoteTestNG.run(IDEARemoteTestNG.java:66)
	at com.intellij.rt.testng.RemoteTestNGStarter.main(RemoteTestNGStarter.java:105)

Just something to keep in mind.