1. A neuron for recognizing a missing input value, comprising: a predetermined number of first inputs for receiving data inputs of the neuron; a plurality of second inputs corresponding to each of said predetermined number of first inputs for receiving null values; each null value being in either a first logic state if a corresponding data input is missing, or a second logic state otherwise; a plurality of nullable weighting elements coupled to said predetermined number of first inputs and to said plurality of second inputs, each nullable weighting element having a weight associated therewith and providing an output thereof as a product of either a corresponding data input and said weight when a corresponding null value is in said first logic state, or as a predetermined value otherwise; a summing device coupled to said plurality of nullable weighting elements, for summing outputs of each nullable weighting element to provide a net output; and an activation element coupled to said summing device, for providing an output of the neuron in response to said net output and a predetermined activation function.