升级成 macOS 11.0 后，给电脑安装 nginx 的时候，发现运行 brew 任何命令都会出现以下错误。

$  brew install nginx
Traceback (most recent call last):
    11: from /usr/local/Homebrew/Library/Homebrew/brew.rb:23:in `<main>'
    10: from /usr/local/Homebrew/Library/Homebrew/brew.rb:23:in `require_relative'
     9: from /usr/local/Homebrew/Library/Homebrew/global.rb:29:in `<top (required)>'
     8: from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
     7: from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
     6: from /usr/local/Homebrew/Library/Homebrew/os.rb:3:in `<top (required)>'
     5: from /usr/local/Homebrew/Library/Homebrew/os.rb:21:in `<module:OS>'
     4: from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:58:in `prerelease?'
     3: from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:24:in `version'
     2: from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:24:in `new'
     1: from /usr/local/Homebrew/Library/Homebrew/os/mac/version.rb:26:in `initialize'
/usr/local/Homebrew/Library/Homebrew/version.rb:368:in `initialize': Version value must be a string; got a NilClass () (TypeError)

解决办法：

只需要在终端输入命令 brew update-reset 。这是最佳办法。 文献：
discourse.brew.sh