  Accompanied by an X-ray burst, the fast radio burst (FRB) FRB 200428 was
recently confirmed as originating from the Galactic magnetar soft gamma
repeater (SGR) SGR J1935+2154. Just before and after FRB 200428 was detected,
the Five-hundred-meter Aperture Spherical radio Telescope (FAST) had been
monitoring SGR J1935+2154 for eight hours. From UTC 2020 April 27 23:55:00 to
2020 April 28 00:50:37, FAST detected no pulsed radio emission from SGR
J1935+2154, while Fermi/Gamma-ray Burst Monitor registered 34 bursts in the
X/soft $\gamma$-ray band, forming a unique sample of X-ray bursts in the
absence of FRBs. After a comprehensive analysis on light curves,
time-integrated, and time-resolved spectral properties of these FRB-absent
X-ray bursts, we compare this sample with the FRB-associated X-ray burst
detected by Insight-HXMT, INTEGRAL, and Konus-Wind. The FRB-associated burst
distinguishes itself from other X-ray bursts by its nonthermal spectrum and a
higher spectral peak energy, but otherwise is not atypical. We also compare the
cumulative energy distribution of our X-ray burst sample with that of first
repeating FRB source, FRB 121102, with the calibration of FRB 200428-X-ray
burst association. We find a similarity between the two, offering indirect
support of the magnetar origin of cosmological FRBs. The event rate density of
magnetar bursts is about $\sim 150$ times higher than the FRB event rate
density at the energy of FRB 200428. This again suggests that, if all FRBs
originate from magnetars, only a small fraction of X-ray bursts are associated
with FRBs.
