Changed processing of whitespace on content properties (#136).

src/main/java/org/gitlab4j/api/AbstractApi.java

@@ -299,8 +299,8 @@ public abstract class AbstractApi implements Constants {
             return;
         }
 
-        String stringValue = value.toString().trim();
-        if (required && stringValue.length() == 0) {
+        String stringValue = value.toString();
+        if (required && stringValue.trim().length() == 0) {
             throw new IllegalArgumentException(name + " cannot be empty or null");
         }