code: public String getErrorReport() {
  		Map<String, List<PropertyMigration>> content = getContent(
  				LegacyProperties::getUnsupported);
  		if (content.isEmpty()) {
  			return null;
  		}
  		StringBuilder report = new StringBuilder();
  		report.append(String.format("%nThe use of configuration keys that are no longer "
  				+ "supported was found in the environment:%n%n"));
  		append(report, content);
  		report.append(String.format("%n"));
  		report.append("Please refer to the migration guide or reference guide for "
  				+ "potential alternatives.");
  		report.append(String.format("%n"));
  		return report.toString();
  	}
docs: Return a report for all the properties that are no longer supported. If no such
  properties were found, return {@code null}.
  @return a report with the configurations keys that are no longer supported