Merge pull request sendgrid#68 from pbdeuchler/cache_string_during_conditionals

Caches email.smtpapi.jsonString() so we only have to call it once

Author: eddiezane

src/main/java/com/sendgrid/SendGrid.java

@@ -139,8 +139,9 @@ public HttpEntity buildBody(Email email) {
     if (email.getText() != null && !email.getText().isEmpty())
       builder.addTextBody(PARAM_TEXT, email.getText(), ContentType.create("text/plain", "UTF-8"));
 
-    if (!email.smtpapi.jsonString().equals("{}"))
-      builder.addTextBody(PARAM_XSMTPAPI, email.smtpapi.jsonString(), ContentType.create("text/plain", "UTF-8"));
+    String tmpString = email.smtpapi.jsonString();
+    if (!tmpString.equals("{}"))
+      builder.addTextBody(PARAM_XSMTPAPI, tmpString, ContentType.create("text/plain", "UTF-8"));
 
     return builder.build();
   }