Add NullInputStream.INSTANCE.

Add @SuppressWarnings("resource").

Author: Gary Gregory

src/changes/changes.xml

@@ -96,6 +96,9 @@ The <action> type attribute can be add,update,fix,remove.
       <action dev="ggregory" type="add" due-to="Gary Gregory">
         Add NullWriter.INSTANCE and deprecate NULL_WRITER.
       </action>
+      <action dev="ggregory" type="add" due-to="Gary Gregory">
+        Add NullInputStream.INSTANCE.
+      </action>
       <!-- UPDATE -->
       <action dev="ggregory" type="update" due-to="Dependabot">
         Bump Maven Javadoc plugin from 3.2.0 to 3.3.0.

src/main/java/org/apache/commons/io/input/NullInputStream.java

@@ -67,6 +67,13 @@
  */
 public class NullInputStream extends InputStream {
 
+    /**
+     * The singleton instance.
+     *
+     * @since 2.12.0
+     */
+    public static final NullInputStream INSTANCE = new NullInputStream();
+
     private final long size;
     private long position;
     private long mark = -1;

src/test/java/org/apache/commons/io/input/ObservableInputStreamTest.java

@@ -253,15 +253,15 @@ public void testDataBytesCalled() throws Exception {
 
     @Test
     public void testGetObservers0() throws IOException {
-        try (final ObservableInputStream ois = new ObservableInputStream(new NullInputStream())) {
+        try (final ObservableInputStream ois = new ObservableInputStream(NullInputStream.INSTANCE)) {
             assertTrue(ois.getObservers().isEmpty());
         }
     }
 
     @Test
     public void testGetObservers1() throws IOException {
         final DataViewObserver observer0 = new DataViewObserver();
-        try (final ObservableInputStream ois = new ObservableInputStream(new NullInputStream(), observer0)) {
+        try (final ObservableInputStream ois = new ObservableInputStream(NullInputStream.INSTANCE, observer0)) {
             assertEquals(observer0, ois.getObservers().get(0));
         }
     }
@@ -270,7 +270,7 @@ public void testGetObservers1() throws IOException {
     public void testGetObserversOrder() throws IOException {
         final DataViewObserver observer0 = new DataViewObserver();
         final DataViewObserver observer1 = new DataViewObserver();
-        try (final ObservableInputStream ois = new ObservableInputStream(new NullInputStream(), observer0, observer1)) {
+        try (final ObservableInputStream ois = new ObservableInputStream(NullInputStream.INSTANCE, observer0, observer1)) {
             assertEquals(observer0, ois.getObservers().get(0));
             assertEquals(observer1, ois.getObservers().get(1));
         }

src/test/java/org/apache/commons/io/output/CloseShieldWriterTest.java

@@ -37,6 +37,7 @@ public class CloseShieldWriterTest {
 
     private Writer shielded;
 
+    @SuppressWarnings("resource")
     @BeforeEach
     public void setUp() {
         original = spy(new StringBuilderWriter());

src/test/java/org/apache/commons/io/test/ThrowOnCloseInputStream.java

@@ -30,9 +30,8 @@ public class ThrowOnCloseInputStream extends ProxyInputStream {
     /**
      * Default ctor.
      */
-    @SuppressWarnings("resource")
     public ThrowOnCloseInputStream() {
-        super(new NullInputStream());
+        super(NullInputStream.INSTANCE);
     }
 
     /**