1. Apparatus for processing data, said apparatus comprising: a stack memory; instruction decoder circuitry, responsive to program instructions, configured to generate control signals; and data processing circuitry, coupled to said stack memory and controlled by said control signals, configured to perform data processing operations upon data values stored in said stack memory, wherein said instruction decoder circuitry, in response to a dedicated null check instruction, is configured to generate control signals that control said data processing circuitry to perform only a dedicated null checking operation and no other operation, the dedicated null checking operation of said instruction decoder circuitry comprising: (i) reading a data value from said stack memory; (ii) comparing said data value with a null value; (iii) if said data value matches said null value, then jumping to execution of a null value exception handler stored at an address independent of said null check instruction; and (iv) if said data value does not match said null value, then proceeding to a next program instruction.