code: public boolean representsNull(FieldDescriptor fld, Object aValue)
      {
          if(aValue == null) return true;
  
          boolean result = false;
          if(((aValue instanceof Number) && (((Number) aValue).longValue() == 0)))
          {
              Class type = fld.getPersistentField().getType();
              /*
              AnonymousPersistentFields will *always* have a null type according to the
              javadoc comments in AnonymousPersistentField.getType() and never represents
              a primitve java field with value 0, thus we return always 'false' in this case.
              (If the value object is null, the first check above return true)
              */
              if(type != null)
              {
                  result = type.isPrimitive();
              }
          }
          // TODO: Do we need this check?? String could be nullified, why should we assume
          // it's 'null' on empty string?
          else if((aValue instanceof String) && (((String) aValue).length() == 0))
          {
              result = fld.isPrimaryKey();
          }
          return result;
      }
docs: Decide if the given object value represents 'null'.<br/>
  
  - If given value is 'null' itself, true will be returned<br/>
  
  - If given value is instance of Number with value 0 and the field-descriptor
  represents a primitive field, true will be returned<br/>
  
  - If given value is instance of String with length 0 and the field-descriptor
  is a primary key, true will be returned<br/>