code: public String determineUsername() {
  		if (StringUtils.hasText(this.username)) {
  			return this.username;
  		}
  		if (EmbeddedDatabaseConnection.isEmbedded(determineDriverClassName())) {
  			return "sa";
  		}
  		return null;
  	}
docs: Determine the username to use based on this configuration and the environment.
  @return the username to use
  @since 1.4.0