TypeError: HiPlot generation failing when optimizing TransitionChoice

[akorb]

Steps to reproduce

Execute the script below.

Observed Results

• TypeError: Object of type int64 is not JSON serializable

Expected Results

• plot.html which shows the HiPlot of the optimization.

Relevant Code

from hiplot import Experiment
import nevergrad as ng
from nevergrad.optimization.callbacks import ParametersLogger
from math import cos

parametrization = ng.p.Instrumentation(
    ng.p.TransitionChoice(10)
)

optimizer = ng.optimizers.NGOpt(parametrization=parametrization, budget=10)

logger = ParametersLogger("log.json")
optimizer.register_callback("tell",  logger)

recommendation = optimizer.minimize(cos)
print("Recommendation: ", recommendation.value)

exp: Experiment = logger.to_hiplot_experiment()
exp.to_html("plot.html")

Notes

The reason that it crashes is that exp.datapoints[0].values['0.indices#0'] is a np.int64 instead of a simple native int.

TransitionChoice has the layer _datalayers.Int. And its _layered_get_value function returns an np.int64.

https://github.com/facebookresearch/nevergrad/blob/8403d6c9659f40fec2a3cf7f474b3d8610f0f2e4/nevergrad/parametrization/_layering.py#L269-L285

Not sure if this is the source of the problem, I'm not familiar with the guts of nevergrad