do not include the token in the signature if it's empty

src/main/java/org/scribe/model/Token.java

@@ -57,4 +57,22 @@ public class Token implements Serializable
   {
     return String.format("Token[%s , %s]", token, secret);
   }
+
+  /**
+   * Returns true if the token is empty (token = "", secret = "")
+   */
+  public boolean isEmpty()
+  {
+    return "".equals(this.token) && "".equals(this.secret);
+  }
+
+  /**
+   * Factory method that returns an empty token (token = "", secret = "").
+   *
+   * Useful for two legged OAuth.
+   */
+  public static Token empty()
+  {
+    return new Token("","");
+  }
 }

src/main/java/org/scribe/oauth/OAuth10aServiceImpl.java

@@ -88,8 +88,12 @@ public class OAuth10aServiceImpl implements OAuthService
   public void signRequest(Token token, OAuthRequest request)
   {
     config.log("signing request: " + request.getCompleteUrl());
-    request.addOAuthParameter(OAuthConstants.TOKEN, token.getToken());
 
+    // Do not append the token if empty. This is for two legged OAuth calls.
+    if (!token.isEmpty())
+    {
+      request.addOAuthParameter(OAuthConstants.TOKEN, token.getToken());
+    }
     config.log("setting token to: " + token);
     addOAuthParams(request, token);
     appendSignature(request);