fix: fix NullOutputStream Javadoc and enhance tests

Author: ppkarwasz

src/main/java/org/apache/commons/io/output/NullOutputStream.java

@@ -69,11 +69,16 @@ public void write(final byte[] b) throws IOException {
     }
 
     /**
-     * Does nothing.
+     * No-op operation.
      *
-     * @param b This method ignores this parameter.
-     * @param off This method ignores this parameter.
-     * @param len This method ignores this parameter.
+     * <p>Validates the arguments but does not write the data.</p>
+     *
+     * @param b   The byte array to write from, not {@code null}.
+     * @param off The offset to start at.
+     * @param len The number of bytes to write.
+     * @throws NullPointerException      If {@code b} is {@code null}.
+     * @throws IndexOutOfBoundsException If {@code off} or {@code len} are negative, {@code off + len} is greater than
+     *                                   {@code b.length}.
      */
     @Override
     public void write(final byte[] b, final int off, final int len) {

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

@@ -16,6 +16,8 @@
  */
 package org.apache.commons.io.output;
 
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
 import java.io.IOException;
 
 import org.junit.jupiter.api.Test;
@@ -34,11 +36,18 @@ private void process(final NullOutputStream nos) throws IOException {
         nos.close();
         nos.write("allowed".getBytes());
         nos.write(255);
+        // Test arguments validation
+        final byte[] b = new byte[1];
+        assertThrows(IndexOutOfBoundsException.class, () -> nos.write(b, -1, 0));
+        assertThrows(IndexOutOfBoundsException.class, () -> nos.write(b, 0, -1));
+        assertThrows(IndexOutOfBoundsException.class, () -> nos.write(b, 0, 2));
+        assertThrows(NullPointerException.class, () -> nos.write(null, 0, 0));
     }
 
     @Test
+    @SuppressWarnings("deprecation")
     void testNewInstance() throws IOException {
-        try (NullOutputStream nos = NullOutputStream.INSTANCE) {
+        try (NullOutputStream nos = new NullOutputStream()) {
             process(nos);
         }
     }