What is the expected enhancement?

The convert method of the gradients takes a params argument specifying for which parameters the gradient should be computed. The error messages and supported input types of that argument vary between Gradient, NaturalGradient, QFI etc. For instance, Gradient.convert supports ParameterVectors but for the others the parameter vector must explicitly be unpacked in a list.

Also the error messages if the argument is missing can be improved. E.g. not passing the argument for the QFI merely raises

KeyError: None