BAEL-6021: Handling NullPointerException in findFirst() When the First Element It Finds Is Null (#15341)

core-java-modules/core-java-streams-5/src/test/java/com/baeldung/findfirstnullpointerexception/FindFirstNullPointerExceptionUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.findfirstnullpointerexception;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.function.Function;
+
+import org.junit.Test;
+
+public class FindFirstNullPointerExceptionUnitTest {
+
+    private final List<String> inputs = Arrays.asList(null, "foo", "bar");
+
+    @Test(expected = NullPointerException.class)
+    public void givenStream_whenCallingFindFirst_thenThrowNullPointerException() {
+        Optional<String> firstElement = inputs.stream()
+          .findFirst();
+    }
+
+    @Test
+    public void givenStream_whenUsingOfNullableBeforeFindFirst_thenCorrect() {
+        Optional<String> firstElement = inputs.stream()
+          .map(Optional::ofNullable)
+          .findFirst()
+          .flatMap(Function.identity());
+
+        assertTrue(firstElement.isEmpty());
+    }
+
+    @Test
+    public void givenStream_whenUsingFilterBeforeFindFirst_thenCorrect() {
+        Optional<String> firstNonNullElement = inputs.stream()
+          .filter(Objects::nonNull)
+          .findFirst();
+
+        assertTrue(firstNonNullElement.isPresent());
+    }
+
+}