A double negation with 无不
“There is not...who doesn’t...”
无不 
is used to make sentences like "There’s not a day I don’t think about it" or "There’s not a man who doesn’t like sweets".
This collocation has the meaning "everybody", "everyone without exception".
is used to make sentences like "There’s not a day I don’t think about it" or "There’s not a man who doesn’t like sweets".
This collocation has the meaning "everybody", "everyone without exception". Pay attention
无不 is used in written speech.
Examples
村里的一草一木我无不熟悉
There’s not a single tree or blade of grass in the village I wouldn’t know
cūnlǐ de yì cǎo yí mù wǒ wú bù shúxī
见此惨状，无不落泪
After seeing such a tragic picture, every single person cried
jiàn cǐ cǎnzhuàng, wú bú luò lèi
听到消息他们无不战战兢兢
They all trembled when they heard the news
tīngdào xiāoxi tāmen wú bú zhànzhànjīngjīng