Fix possible exception in toCamelCase method

src/main/java/org/elasticsearch/common/Strings.java

@@ -1425,7 +1425,9 @@ public class Strings {
                     }
                     changed = true;
                 }
-                sb.append(Character.toUpperCase(value.charAt(++i)));
+                if (i < value.length() - 1) {
+                    sb.append(Character.toUpperCase(value.charAt(++i)));
+                }
             } else {
                 if (changed) {
                     sb.append(c);

src/test/java/org/elasticsearch/common/StringsTests.java

@@ -0,0 +1,36 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch 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.elasticsearch.common;
+
+import org.elasticsearch.test.ElasticsearchTestCase;
+import org.junit.Test;
+
+public class StringsTests extends ElasticsearchTestCase {
+
+    @Test
+    public void testToCamelCase() {
+        assertEquals("foo", Strings.toCamelCase("foo"));
+        assertEquals("fooBar", Strings.toCamelCase("fooBar"));
+        assertEquals("FooBar", Strings.toCamelCase("FooBar"));
+        assertEquals("fooBar", Strings.toCamelCase("foo_bar"));
+        assertEquals("fooBarFooBar", Strings.toCamelCase("foo_bar_foo_bar"));
+        assertEquals("fooBar", Strings.toCamelCase("foo_bar_"));
+    }
+}