ULN2803A Input Pull-Downs
The emitter can never be open with respect to the base as there are internal resistors etc., so Icbo is inappropriate. Leakage can occur from the collector to base of the input transistor. That is shunted away by the series resistors so it doesn't turn the output transistor on and no significant voltage appears at the input. 



Icex is the parameter (50uA maximum). Figure 4. Icex test circuit illustrates the circuit with input open.