code: private void get_class_system_resource() {
  
          //
          // Try to retrieve the class resource doc_url
          //
  
          if (Util._UseDb) {
              try {
  
                  //
                  // Call db server
                  //
  
                  final DbDatum res_value = db_class.get_property("doc_url");
  
                  if (res_value.is_empty() == true) {
                      Util.out4.println("doc_url property for class " + name
                              + " is not defined in database");
                      doc_url = Tango_DefaultDocUrl;
                  } else {
                      doc_url = res_value.extractString();
                  }
              } catch (final DevFailed ex) {
                  doc_url = Tango_DefaultDocUrl;
              } catch (final BAD_OPERATION ex) {
                  doc_url = Tango_DefaultDocUrl;
              }
          } else {
              doc_url = Tango_DefaultDocUrl;
          }
      }
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