code: public OAuthHmacCredential load10aCredential(String userId) throws IOException {
          if (getCredentialStore() == null) {
              return null;
          }
          OAuthHmacCredential credential = new10aCredential(userId);
          if (!getCredentialStore().load(userId, credential)) {
              return null;
          }
          return credential;
      }
docs: Loads the OAuth 1.0a credential of the given user ID from the credential
  store.
  
  @param userId user ID or {@code null} if not using a persisted credential
  store
  @return OAuth 1.0a credential found in the credential store of the given
  user ID or {@code null} for none found