code: private boolean shouldInterpretEmptyStringSubmittedValuesAsNull(FacesContext context)
      {
          ExternalContext ec = context.getExternalContext();
          Boolean interpretEmptyStringAsNull
                  = (Boolean)ec.getApplicationMap().get(MYFACES_EMPTY_VALUES_AS_NULL_PARAM_NAME);
  
          // not yet cached...
          if (interpretEmptyStringAsNull == null)
          {
              // parses the web.xml to get the "javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL" value
              String param = ec.getInitParameter(EMPTY_VALUES_AS_NULL_PARAM_NAME);
  
              // evaluate the param
              interpretEmptyStringAsNull = "true".equalsIgnoreCase(param);
  
              // cache the parsed value
              ec.getApplicationMap().put(MYFACES_EMPTY_VALUES_AS_NULL_PARAM_NAME, interpretEmptyStringAsNull);
          }
  
          return interpretEmptyStringAsNull;
      }
docs: Checks if the <code>validate()</code> should interpret an empty
  submitted value should be handle as <code>NULL</code>
  
  @return a (cached) boolean to identify the interpretation as null