Non-anti-aliasing components (AWT, Swing Motif and Nimbus L&F) don't show some line shaped characters. For example, U+007C (VERTICAL LINE), or U+00A6 (BROKEN BAR).

This problem was found by an AWT application originally.
So, our team created a check program to find empty drawing.
The following list is a part of problematic conditions we found.
This problem depends on font's size.

Since this problem was recreated by FreeType's demo application (ftview),
I reported it to FreeType as well.
https://savannah.nongnu.org/bugs/index.php?54589

-- Check results --
Checked from 10 points to 24 points. FreeType library in bundled was used.
(Removed font's problems, such as lacking the bitmap glyph, etc.)

*OpenSans-Light.ttf
https://fonts.google.com/specimen/Open+Sans
size:22 \u007c\u00a6

*FreeSans.ttf
http://www.gnu.org/software/freefont/
size:10 \u02c5\u02ef
size:11 \u02c5\u02ef\u23a5
size:12 \u2595
size:15 \u22ee

*VL-Gothic-Regular.ttf
http://dicey.org/vlgothic
size:12 \u02c8\u02cc\u02d9\u2f01\u4e28
size:22 \u2502\u2506\u250a\u254e\u2575\u2577

*NotoSansCJKjp-Regular.otf
https://www.google.com/get/noto/
size:10 \u2010\u2504\u2508\u250a\ufe32\ufe49\ufe4a\ufe4d\ufe4e
size:11 \u2508\u2b1a\u2ff1\u2ff2\u2ff3\u2ffb\ufe49\ufe4d
size:12 \u2504\u250a\u2b1a\u2ff0\u2ff1\u2ff2\u2ff3\u2ff4\u2ff9
size:13 \u2b1a\u2ff1\u2ff3\u2ff4\u2ff5\u2ff6\u2ff7\u2ff8\u2ff9\u2ffa
size:14 \u2b1a\u2ff0\u2ff1\u2ff2\u2ff3\u2ff4
size:15 \u2b1a\u2ff1\u2ff3\u2ffb