code: protected void logKeyFound(String key, PropertySource<?> propertySource, Object value) {
          if (logger.isDebugEnabled()) {
              logger.debug("Found key '" + key + "' in PropertySource '" + propertySource.getName()
                           + "' with value of type " + value.getClass().getSimpleName());
          }
      }
docs: Log the given key as found in the given {@link PropertySource}, resulting in
  the given value.
  <p>
  The default implementation writes a debug log message with key and source. As
  of 4.3.3, this does not log the value anymore in order to avoid accidental
  logging of sensitive settings. Subclasses may override this method to change
  the log level and/or log message, including the property's value if desired.
  
  @param key the key found
  @param propertySource the {@code PropertySource} that the key has been found
  in
  @param value the corresponding value
  @since 4.3.1