Environments:

• Prettier Version: 1.15.1
• Running Prettier via: CLI
• Runtime: node 11.1.0
• Operating System: macOS 10.14

Steps to reproduce:

$ echo '{"name": "a-package"}' > ./package.json
$ prettier --tab-width 2 --use-tabs --tab-width 4 ./package.json

Expected behavior:

$ prettier --tab-width 2 --use-tabs --tab-width 4 ./package.json
{
	"name": "a-package"
}

Actual behavior:

$ prettier --tab-width 2 --use-tabs --tab-width 4 package.json
[error] Invalid --tab-width value. Expected an integer, but received null.

I happen to find myself in a situation where I need to override a CLI flag with another one, which appended to the invocation later. I cannot just remove the first flag, unfortunately.

What I would expect would be for Prettier to use the last value given for a flag, instead of trying to combine them into an array? (At least, I think that's what minimist is doing; I'm not sure where the error about "null" is coming from.)