#vulnerable code 
                              @SuppressWarnings("unused")
  public ListBoxModel doFillCredentialsIdItems(@QueryParameter String credentialsId) {
    if (!Jenkins.getInstance().hasPermission(Jenkins.ADMINISTER)) {
      return new StandardListBoxModel().includeCurrentValue(credentialsId);
    }

    return new StandardListBoxModel()
      .includeEmptyValue()
      .includeMatchingAs(
        ACL.SYSTEM,
        Jenkins.getInstance(),
        StringCredentials.class,
        Collections.emptyList(),
        CredentialsMatchers.always()
      );
  } 
                            #location 3 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              @SuppressWarnings("unused")
  public ListBoxModel doFillCredentialsIdItems(@QueryParameter String credentialsId) {
    return createListBoxModel(credentialsId);
  }