Value for SWIFT_VERSION cannot be empty
You need to search for every "PRODUCT_NAME ="
There needs to be a " SWIFT_VERSION = "4.2"; " after everyone.
eg. also PRODUCT_NAME = "$(TARGET_NAME)";enter code here
In case there is anybody else reading through this thread who has this same problem but was unable to solve it using the above answers, this may help:
If you have a data model, you need to check that when you click on the data model, click on an entity, and bring up the file inspector, the "Code Generation" Language is properly set. In my case my whole app was written Objective-C, but was set here to Swift for some reason. This is another reason that Error will show up in the Issue Navigator.
It's very important to clear the build folder after changing Code Generation Language. This can be done by pressing Command-Shift-K or by clicking Product->Clean Build Folder in the menu at the top of the screen.
Check out this link for a picture of where to find the "Code Generation" option I'm talking about.
Model.xcdatamodeld->File Inspector->Code Generation
Update for Xcode 10.2
Go to --> Build Setting
Select All + Combined or All + Levels underneath the Build Settings
And Finally on the search bar, on the right hand side search for "Swift Language Version"
Select your app target then goto build setting, search for swift set the swift language version from the dropdown.
