Many times, the "briefcase" generators like Honda and Yamaha won't charge an electric car if the EVSE can't sense a ground. With a simple plug in any outlet of the generator wired to have a teeny, tiny path of current from hot to ground, this will enable the generator to sense ground, and therefore charge the car.
The easy way to make this work is take a NEMA 5-15P plug and install two 1/2 watt 100k ohm resistors. One from neutral to ground (usually green), and the other from hot to ground. Then simply plug this into any outlet on the generator, and your EVSE into the other outlet. This will safely pass the ground detect on the EVSE, while not being a hazard in any other way.
If charging from a 240 volt generator, connect both hot legs and the neutral to ground. Then earth is then properly floating in the "middle".
Contrary to many folks here, I do NOT own a LEAF.