RuntimeError: Can not put single artist in more than one figure

importmatplotlib.pyplotaspltimportnumpyasnpimportmatplotlib.tickerasmtickeryear= [1950,1960,1970,1980,1990,2000,2010,2018]population_by_continent= {"Africa": [0.228,0.284,0.365,0.477,0.631,0.814,1.044,1.275],"the Americas": [0.340,0.425,0.519,0.619,0.727,0.840,0.943,1.006],"Asia": [1.394,1.686,2.120,2.625,3.202,3.714,4.169,4.560],"Europe": [0.220,0.253,0.276,0.295,0.310,0.303,0.294,0.293],"Oceania": [0.012,0.015,0.019,0.022,0.026,0.031,0.036,0.039],}fig=plt.figure()subfigs=fig.subfigures(nrows=1,ncols=2)for_figinsubfigs:axs=_fig.subplots(nrows=2,ncols=1,squeeze=False)[0]foraxinaxs:ax.stackplot(year,population_by_continent.values(),labels=population_by_continent.keys(),alpha=0.8,        )ax.legend(loc="upper left",reverse=True)ax.set_title("World population")ax.set_xlabel("Year")ax.set_ylabel("Number of people (billions)")# add tick at every 200 million peopleax.yaxis.set_minor_locator(mticker.MultipleLocator(0.2))fig.legend(loc="upper right",bbox_to_anchor=(1.1,1))# error!