Adding validation to Region class

core/src/main/java/software/amazon/awssdk/core/regions/Region.java

@@ -19,6 +19,7 @@
 import java.util.Collections;
 import java.util.List;
 import software.amazon.awssdk.utils.AbstractEnum;
+import software.amazon.awssdk.utils.Validate;
 
 /**
  * An Amazon Web Services region that hosts a set of Amazon services.
@@ -120,10 +121,11 @@ private Region(String value) {
      * For example, the following conditions will always evaluated to true:
      * {@code Region.of("us-east-1") == Region.of("us-east-1")}, {@code Region.US_EAST_1 == Region.of("us-east-1")}.</p>
      *
-     * @param value The name of the region to load.
+     * @param value The name of the region to load. Can't be null, empty or blank
      * @return The region associated with the provided name.
      */
     public static Region of(String value) {
+        Validate.paramNotBlank(value, "region");
         return AbstractEnum.value(value, Region.class, Region::new);
     }
 

core/src/test/java/software/amazon/awssdk/core/regions/RegionTest.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2010-2017 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file 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 software.amazon.awssdk.core.regions;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class RegionTest {
+
+    @Test(expected = NullPointerException.class)
+    public void of_ThrowsNullPointerException_WhenNullValue() {
+        Region.of(null);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void of_ThrowsIllegalArgumentException_WhenEmptyString() {
+        Region.of("");
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void of_ThrowsIllegalArgumentException_WhenBlankString() {
+        Region.of(" ");
+    }
+
+    @Test
+    public void of_ReturnsRegion_WhenValidString() {
+        Region region = Region.of("us-east-1");
+        assertThat(region.value()).isEqualTo("us-east-1");
+    }
+}

utils/src/main/java/software/amazon/awssdk/utils/Validate.java

@@ -140,6 +140,30 @@ public static <T> T paramNotNull(final T object, final String paramName) {
         return object;
     }
 
+    /**
+     * <p>Validate that the specified char sequence is neither
+     * {@code null}, a length of zero (no characters), empty nor
+     * whitespace; otherwise throwing an exception with the specified
+     * message.
+     *
+     * <pre>Validate.paramNotBlank(myCharSequence, "myCharSequence");</pre>
+     *
+     * @param <T> the char sequence type
+     * @param chars  the character sequence to check
+     * @param paramName  The name of the param or field being checked.
+     * @return the validated char sequence (never {@code null} for method chaining)
+     * @throws NullPointerException if the char sequence is {@code null}
+     */
+    public static <T extends CharSequence> T paramNotBlank(final T chars, final String paramName) {
+        if (chars == null) {
+            throw new NullPointerException(String.format("%s must not be null.", paramName));
+        }
+        if (StringUtils.isBlank(chars)) {
+            throw new IllegalArgumentException(String.format("%s must not be blank or empty.", paramName));
+        }
+        return chars;
+    }
+
     /**
      * <p>Validate the stateful predicate is true for the given object and return the object;
      * otherwise throw an exception with the specified message.</p>