Should check if positional_params is nil or not

[ksss]

The following code raises an unexpected error.

[].each(*a)

Unexpected error: #<NoMethodError: undefined method `each' for nil:NilClass>
/Users/ksss/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/steep-0.46.0/lib/steep/type_inference/send_args.rb:156:in `uniform_type'
/Users/ksss/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/steep-0.46.0/lib/steep/type_inference/send_args.rb:567:in `block in each'
...

[soutaro]

👍