Fix NullPointerException in ReflectionDiffBuilder.getExcludeFieldNames()

when instance created with
ReflectionDiffBuilder.ReflectionDiffBuilder(T, T, ToStringStyle)

Author: garydgregory

src/changes/changes.xml

@@ -64,6 +64,7 @@ The <action> type attribute can be add,update,fix,remove.
     <action                   type="fix" dev="ggregory" due-to="Gary Gregory">Fix Apache RAT plugin console warnings.</action>
     <action issue="LANG-1793" type="fix" dev="ggregory" due-to="IcoreE">Fix Javadoc description in CharUtils.isAsciiAlphanumeric() #1501.</action>
     <action issue="LANG-1794" type="fix" dev="ggregory" due-to="IcoreE">Fix Javadoc for RandomUtils.secure(), it incorrectly mentions securerandom.strongAlgorithms #1503.</action>
+    <action                   type="fix" dev="ggregory" due-to="Gary Gregory">Fix NullPointerException in ReflectionDiffBuilder.getExcludeFieldNames() when instance created with ReflectionDiffBuilder.ReflectionDiffBuilder(T, T, ToStringStyle).</action>
     <!-- ADD -->
     <!-- UPDATE -->
     <action                   type="update" dev="ggregory" due-to="Gary Gregory, Dependabot">Bump org.apache.commons:commons-parent from 92 to 93 #1498.</action>

src/main/java/org/apache/commons/lang3/builder/ReflectionDiffBuilder.java

@@ -19,6 +19,7 @@
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.util.Arrays;
+import java.util.Objects;
 
 import org.apache.commons.lang3.ArraySorter;
 import org.apache.commons.lang3.ArrayUtils;
@@ -155,7 +156,7 @@ private static String[] toExcludeFieldNames(final String[] excludeFieldNames) {
 
     private ReflectionDiffBuilder(final DiffBuilder<T> diffBuilder, final String[] excludeFieldNames) {
         this.diffBuilder = diffBuilder;
-        this.excludeFieldNames = excludeFieldNames;
+        this.excludeFieldNames = Objects.requireNonNull(excludeFieldNames);
     }
 
     /**
@@ -174,7 +175,7 @@ private ReflectionDiffBuilder(final DiffBuilder<T> diffBuilder, final String[] e
      */
     @Deprecated
     public ReflectionDiffBuilder(final T left, final T right, final ToStringStyle style) {
-        this(DiffBuilder.<T>builder().setLeft(left).setRight(right).setStyle(style).build(), null);
+        this(DiffBuilder.<T>builder().setLeft(left).setRight(right).setStyle(style).build(), ArrayUtils.EMPTY_STRING_ARRAY);
     }
 
     private boolean accept(final Field field) {
@@ -187,7 +188,7 @@ private boolean accept(final Field field) {
         if (Modifier.isStatic(field.getModifiers())) {
             return false;
         }
-        if (this.excludeFieldNames != null && Arrays.binarySearch(this.excludeFieldNames, field.getName()) >= 0) {
+        if (excludeFieldNames != null && Arrays.binarySearch(excludeFieldNames, field.getName()) >= 0) {
             // Reject fields from the getExcludeFieldNames list.
             return false;
         }
@@ -236,7 +237,7 @@ public DiffResult<T> build() {
      * @since 3.13.0
      */
     public String[] getExcludeFieldNames() {
-        return this.excludeFieldNames.clone();
+        return excludeFieldNames.clone();
     }
 
     private T getLeft() {

src/test/java/org/apache/commons/lang3/builder/ReflectionDiffBuilderTest.java

@@ -146,6 +146,14 @@ void testDifferenceInInherited_field() {
         assertEquals(1, list.getNumberOfDiffs());
     }
 
+    @Test
+    void testGetExcludeFieldNamesEmpty() {
+        final ReflectionDiffBuilder reflectionDiffBuilder = new ReflectionDiffBuilder(new TypeTestClass(), new TypeTestChildClass(), SHORT_STYLE);
+        final String[] excludeFieldNames = reflectionDiffBuilder.getExcludeFieldNames();
+        assertNotNull(excludeFieldNames);
+        assertEquals(0, excludeFieldNames.length);
+    }
+
     @Test
     void testGetExcludeFieldNamesWithNullExcludedFieldNames() {
         // @formatter:off