Zoom into SN 2016hnk spectra around the Na I D doublet (rest-frame 5890 and 5896 Å; in vertical black dotted lines) absorption, at seven epochs from +2.5 to +59.7 days after maximum. Thick lines represent Na I D absorption with pEW = 1.3 Å at the spectral resolution of each spectrum. Red vertical lines indicate the position where the Na I D doublet from the Milky Way should be found. In all cases, we do not detect the Na I D lines in SN 2016hnk spectra.