code: public @CheckForNull
      InstructionHandle getSuccessorOf(InstructionHandle handle) {
          if (VERIFY_INTEGRITY && !containsInstruction(handle)) {
              throw new IllegalStateException();
          }
          return handle == lastInstruction ? null : handle.getNext();
      }
docs: Get the successor of given instruction within the basic block.
  
  @param handle
  the instruction
  @return the instruction's successor, or null if the instruction is the
  last in the basic block