  We characterize the occurrence rate of planets, ranging in size from 0.5-16
R$_\oplus$, orbiting FGK stars with orbital periods from 0.5-500 days. Our
analysis is based on results from the "DR25" catalog of planet candidates
produced by NASA's Kepler mission and stellar radii from Gaia "DR2". We
incorporate additional Kepler data products to accurately characterize the
efficiency of planets being recognized as a "threshold crossing events" (TCE)
by Kepler's Transiting Planet Search pipeline and labeled as a planet candidate
by the robovetter. Using a hierarchical Bayesian model, we derive planet
occurrence rates for a wide range of planet sizes and orbital periods. For
planets with sizes $0.75-1.5$ R$_\oplus$ and orbital periods of 237-500 days,
we find a rate of planets per FGK star of $<0.27$ ($84.13$th percentile). While
the true rate of such planets could be lower by a factor of $\sim~2$ (primarily
due to potential contamination of planet candidates by false alarms), the upper
limits on the occurrence rate of such planets are robust to $\sim~10\%$. We
recommend that mission concepts aiming to characterize potentially rocky
planets in or near the habitable zone of sun-like stars prepare compelling
science programs that would be robust for a true rate in the range $f_{R,P} = $
$0.03-0.40$ for $0.75-1.5$ R$_\oplus$ planets with orbital periods in 237-500
days, or a differential rate of $\Gamma_\oplus \equiv (d^2 f)/[d(\ln P)~d(\ln
R_{p})] = $ $0.06-0.76$.
