EyeonTips:Script/Reference/Applications/Fusion/Classes/Operator/GetInputList

From VFXPedia

• The input_type parameter can also be "Mask". However, this will also return the regular image inputs, since masks can be connected to them. Garbage matte inputs won't get returned by GetInputList("Image") though, so the "Mask" parameter might be useful occasionally. To retrieve the effect mask input, you need to scan the attributes of the returned inputs for INPS_ID == "EffectMask".