Fixes NPE when not specifying language.

Author: gguuss

language/analysis/src/main/java/com/google/cloud/language/samples/AnalyzeBeta.java

@@ -131,12 +131,19 @@ public static void printEntities(PrintStream out, List<Entity> entities) {
    * Gets {@link Sentiment} from the string {@code text}.
    */
   public Sentiment analyzeSentimentText(String text, String lang) throws IOException {
-  // NL autodetects the language
-
     // Note: This does not work on App Engine standard.
-    Document doc = Document.newBuilder()
-        .setLanguage(lang)
-        .setContent(text).setType(Type.PLAIN_TEXT).build();
+    // NL autodetects the language
+    Document doc;
+    if (lang != null) {
+      doc = Document.newBuilder()
+          .setLanguage(lang)
+          .setContent(text).setType(Type.PLAIN_TEXT)
+          .build();
+    } else {
+      doc = Document.newBuilder()
+          .setContent(text).setType(Type.PLAIN_TEXT)
+          .build();
+    }
     AnalyzeSentimentResponse response = languageApi.analyzeSentiment(doc);
     return response.getDocumentSentiment();
   }