An empty string '' must pass to the component like an empty string.
It's type cast type to boolean true
It seems that if types validation includes String and Boolean together, we should not check here for the blank line.
There is another case when we have hyphenated string that looks like a prop.
don`t cast empty string to Boolean if prop types include String and B…
…oolean (fix #4538)
…oolean (fix #4538) (#4539)