Add FailableSupplieSuppliersr.nul()

src/changes/changes.xml

@@ -72,6 +72,7 @@ The <action> type attribute can be add,update,fix,remove.
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add LazyInitializer.isInitialized().</action>
     <action                   type="add" dev="ggregory" due-to="Benjamin Confino, Gary Gregory">Add ConcurrentInitializer#isInitialized() #1120.</action>
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add Streams.failableStream(T...).</action>
+    <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add FailableSupplier.nul().</action>
     <!-- UPDATE -->
     <action                   type="update" dev="ggregory" due-to="Gary Gregory">Bump commons-parent from 58 to 64.</action>
     <action                   type="update" dev="ggregory" due-to="Gary Gregory">Bump org.easymock:easymock from 5.1.0 to 5.2.0 #1104.</action>

src/main/java/org/apache/commons/lang3/function/FailableSupplier.java

@@ -29,6 +29,33 @@ import java.util.function.Supplier;
 @FunctionalInterface
 public interface FailableSupplier<R, E extends Throwable> {
 
+    /**
+     * Returns the singleton supplier that always returns null.
+     * <p>
+     * This supplier never throws an exception.
+     * </p>
+     *
+     * @since 3.14.0
+     */
+    @SuppressWarnings("rawtypes")
+    FailableSupplier NUL = () -> null;
+
+    /**
+     * Returns the singleton supplier that always returns null.
+     * <p>
+     * This supplier never throws an exception.
+     * </p>
+     *
+     * @param <T> Supplied type.
+     * @param <E> The kind of thrown exception or error.
+     * @return The NUL singleton.
+     * @since 3.14.0
+     */
+    @SuppressWarnings("unchecked")
+    static <T, E extends Exception> FailableSupplier<T, E> nul() {
+        return NUL;
+    }
+
     /**
      * Supplies an object
      *

src/test/java/org/apache/commons/lang3/function/FailableSupplierTest.java

@@ -0,0 +1,48 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.lang3.function;
+
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests {@link FailableSupplier}.
+ */
+public class FailableSupplierTest {
+
+    @Test
+    public void testNULL() throws Throwable {
+        assertNull(FailableSupplier.NUL.get());
+    }
+
+    @Test
+    public void testNullSupplierDefaultException() throws Exception {
+        assertNull(FailableSupplier.nul().get());
+    }
+
+    @Test
+    public void testNullSupplierException() throws Exception {
+        assertNull(FailableSupplier.<Object, Exception>nul().get());
+    }
+
+    @Test
+    public void testNullSupplierRuntimeException() {
+        assertNull(FailableSupplier.<Object, RuntimeException>nul().get());
+    }
+}

src/test/java/org/apache/commons/lang3/function/ObjectsTest.java

@@ -81,7 +81,7 @@ public class ObjectsTest extends AbstractLangTest {
 
     @Test
     void testRequireNonNullObjectFailableSupplierString() {
-        final TestableFailableSupplier<String, ?> supplier = new TestableFailableSupplier<>(() -> null);
+        final TestableFailableSupplier<String, ?> supplier = new TestableFailableSupplier<>(FailableSupplier.nul());
         assertSame("foo", Objects.requireNonNull("foo", supplier));
         assertFalse(supplier.isInvoked());
         try {
@@ -91,7 +91,7 @@ public class ObjectsTest extends AbstractLangTest {
             assertEquals("The supplier must not return null.", e.getMessage());
             assertTrue(supplier.isInvoked());
         }
-        final TestableFailableSupplier<String, ?> supplier2 = new TestableFailableSupplier<>(() -> null);
+        final TestableFailableSupplier<String, ?> supplier2 = new TestableFailableSupplier<>(FailableSupplier.nul());
         try {
             Objects.requireNonNull(null, supplier2);
             fail("Expected Exception");