code: @Override
  	public String getValue(String key) {
  		return env.get(key.replace('.', '_').toUpperCase());
  	}
docs: Returns the configuration value from the the operating system's environment variables.
  <p>
  Because of the naming restrictions/conventions of environment variables, all dots ('.') are replaced with underscores
  and all letters are converted to upper case.
  <p>
  Example: To set the configuration key <code>stagemonitor.active</code>, the environment variable has to be
  <code>STAGEMONITOR_ACTIVE</code>
  
  @param key the property key
  @return the value