[ruby/tmpdir] Reject empty parent path

https://github.com/ruby/tmpdir/commit/628c5bdc59

lib/tmpdir.rb

@@ -148,7 +148,11 @@ class Dir
     # Generates and yields random names to create a temporary name
     def create(basename, tmpdir=nil, max_try: nil, **opts)
       origdir = tmpdir
-      tmpdir ||= tmpdir()
+      if tmpdir
+        raise ArgumentError, "empty parent path" if tmpdir.empty?
+      else
+        tmpdir = tmpdir()
+      end
       n = nil
       prefix, suffix = basename
       prefix = (String.try_convert(prefix) or

test/test_tmpdir.rb

@@ -104,6 +104,12 @@ class TestTmpdir < Test::Unit::TestCase
     end
   end
 
+  def test_mktmpdir_not_empty_parent
+    assert_raise(ArgumentError) do
+      Dir.mktmpdir("foo", "")
+    end
+  end
+
   def assert_mktmpdir_traversal
     Dir.mktmpdir do |target|
       target = target.chomp('/') + '/'