JCLOUDS-625: Set VolumeBuilder id to nullable in VolumeImpl

VolumeBuilder does not allow null id while VolumeImpl allows it to be nullable.

compute/src/main/java/org/jclouds/compute/domain/VolumeBuilder.java

@@ -24,6 +24,7 @@ import org.jclouds.javax.annotation.Nullable;
 public class VolumeBuilder {
 
    private Volume.Type type;
+   @Nullable
    private String id;
    @Nullable
    private Float size;
@@ -38,7 +39,7 @@ public class VolumeBuilder {
    }
 
    public VolumeBuilder id(String id) {
-      this.id = checkNotNull(id, "id");
+      this.id = id;
       return this;
    }
 

compute/src/main/java/org/jclouds/compute/domain/internal/VolumeImpl.java

@@ -27,6 +27,7 @@ import com.google.common.base.Objects.ToStringHelper;
 
 public class VolumeImpl implements Volume {
 
+   @Nullable
    private final String id;
    private final Volume.Type type;
    @Nullable

compute/src/test/java/org/jclouds/compute/domain/VolumeBuilderTest.java

@@ -0,0 +1,43 @@
+/*
+ * 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.jclouds.compute.domain;
+
+import static org.testng.Assert.assertNull;
+
+import org.jclouds.compute.domain.Volume.Type;
+import org.testng.annotations.Test;
+
+/**
+ * Unit tests for org.jclouds.compute.domain.VolumeBuilder
+ */
+@Test(testName = "VolumeBuilderTest", groups = "unit")
+public class VolumeBuilderTest {
+
+    /**
+     * Ensures that an explicitly set null id results in no errors.
+     */
+    public void testNullDescription() {
+        Volume vol = new VolumeBuilder().id(null)
+                .type(Type.LOCAL)
+                .size(10.0f)
+                .device("/dev/sda1")
+                .bootDevice(true)
+                .durable(false)
+                .build();
+        assertNull(vol.getId());
+    }
+}