Refactoring/Small changes

src/main/java/com/microsoft/bingads/ApiEnvironment.java

@@ -1,5 +1,7 @@
 package com.microsoft.bingads;
 
+import java.util.Arrays;
+
 /**
  * Represents Bing Ads API environment (Production or Sandbox).
  */
@@ -26,11 +28,7 @@ public String value() {
     }
 
     public static ApiEnvironment fromValue(String v) {
-        for (ApiEnvironment c : ApiEnvironment.values()) {
-            if (c.value.equals(v)) {
-                return c;
-            }
-        }
-        throw new IllegalArgumentException(v);
+        return Arrays.stream(values()).filter((env) -> env.value.equals(v)).findFirst()
+                .orElseThrow(() -> new IllegalArgumentException(v));
     }
 }

src/main/java/com/microsoft/bingads/AsyncCallback.java

@@ -7,6 +7,7 @@
  *
  * @param <T> the type of result
  */
+@FunctionalInterface
 public interface AsyncCallback<T> {
 
     /**

src/main/java/com/microsoft/bingads/ServiceClient.java

@@ -140,9 +140,7 @@ public List<Handler> getHandlerChain(PortInfo portInfo) {
             }
         });
 
-        T port = serviceFactory.createProxyFromService(service, environment, serviceInterface);
-
-        return port;
+        return serviceFactory.createProxyFromService(service, environment, serviceInterface);
     }
 
     private void refreshOAuthTokensIfNeeded() {