"So the font, does not map missing characters to a glyph id 0, missing glyph id, but instead maps it to a glyph named '.null', glyph id 12505."
The result is that when Chrome tries to display the Korean characters listed at http://www.alanwood.net/unicode/hangul-jamo-extended-b.html the characters come out as blank.
Please consider to use google-noto-sans-cjk-ttc-fonts and google-noto-serif-cjk-ttc-fonts.
And report this issue to font maintainers - http://kldp.net/baekmuk/ .
There is also naver-nanum-fonts.