'Only search in existing fields'

def getFieldByAddress(self, address, feed=True):

    if (feed and (self._field_generator is not None)):
        self._feedAll()
    if (address < self._current_size):
        i = lowerBound(self._fields.values, (lambda x: ((x.address + x.size) <= address)))
        if (i is not None):
            return self._fields.values[i]
    return None
