1、NoMethodError - undefined method `size’ for nil:NilClass

### Error

​```
NoMethodError - undefined method `size' for nil:NilClass
/Users/su/.rvm/rubies/ruby-2.4.1/lib/ruby/gems/2.4.0/gems/ruby-macho-1.4.0/lib/macho/macho_file.rb:455:in `populate_mach_header'
/Users/su/.rvm/rubies/ruby-2.4.1/lib/ruby/gems/2.4.0/gems/ruby-macho-1.4.0/lib/macho/macho_file.rb:233:in `populate_fields'
/Users/su/.rvm/rubies/ruby-2.4.1/lib/ruby/gems/2.4.0/gems/ruby-macho-1.4.0/lib/macho/macho_file.rb:55:in `initialize_from_bin'
/Users/su/.rvm/rubies/ruby-2.4.1/lib/ruby/gems/2.4.0/gems/ruby-macho-1.4.0/lib/macho/macho_file.rb:33:in `new_from_bin'
/Users/su/.rvm/rubies/ruby-2.4.1/lib/ruby/gems/2.4.0/gems/ruby-macho-1.4.0/lib/macho/fat_file.rb:365:in `block in populate_machos'
...
...
...
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[!] Oh no, an error occurred.
...
...

解决方案来源：https://github.com/CocoaPods/CocoaPods/issues/8377

flutter clean
rm -Rf ios/Pods
rm -Rf ios/.symlinks
rm -Rf ios/Flutter/Flutter.framework
rm -Rf ios/Flutter/Flutter.podspec

2、 iOS使用纯OC开发的项目导入Swift模块

1. 创建一个Swift文件，名称随意
2. 根据提示选择Create Bridging Header。如果没有提示，请自行搜索如何创建。