code: public String getUsername() {
          final String username = basicJdbcConfiguration.getConfiguredUsername();
          if (calculatedUsername == null || StringUtils.hasText(username)) {
              calculatedUsername = username;
              if (!StringUtils.hasText(calculatedUsername) && JdbcDatabaseManager.isEmbedded(basicJdbcConfiguration.getDriverClassName())) {
                  calculatedUsername = "sa";
              }
          }
  
          return calculatedUsername;
      }
docs: Determines the username based on the configured value. If the
  username is not configured and an embedded database driver is
  on the classpath, return 'sa'.
  
  @return The calculated username