Fixes #11207: Do not validate checksums if options are empty string

Prior to this commit, if Vagrant received checksum options from Vagrant
Cloud that were simply empty strings, it would try to validate its
checksum with those options. This commit fixes that by ignoring empty
string values.

lib/vagrant/action/builtin/box_add.rb

@@ -348,9 +348,15 @@ module Vagrant
             end
 
             if opts[:checksum] && opts[:checksum_type]
-              env[:ui].detail(I18n.t("vagrant.actions.box.add.checksumming"))
-              validate_checksum(
-                opts[:checksum_type], opts[:checksum], box_url)
+              if opts[:checksum].to_s.strip.empty?
+                @logger.warn("Given checksum is empty, cannot validate checksum for box")
+              elsif opts[:checksum_type].to_s.strip.empty?
+                @logger.warn("Given checksum type is empty, cannot validate checksum for box")
+              else
+                env[:ui].detail(I18n.t("vagrant.actions.box.add.checksumming"))
+                validate_checksum(
+                  opts[:checksum_type], opts[:checksum], box_url)
+              end
             end
 
             # Add the box!

lib/vagrant/util/file_checksum.rb

@@ -66,7 +66,8 @@ class FileChecksum
     digest = CHECKSUM_MAP[type.to_s.to_sym]
     if digest.nil?
       raise Vagrant::Errors::BoxChecksumInvalidType,
-        type: type.to_s
+        type: type.to_s,
+        types: CHECKSUM_MAP.keys.join(', ')
     end
     digest
   end

templates/locales/en.yml

@@ -578,7 +578,7 @@ en:
         The specified checksum type is not supported by Vagrant: %{type}.
         Vagrant supports the following checksum types:
 
-        md5, sha1, sha256
+        %{types}
       box_checksum_mismatch: |-
         The checksum of the downloaded box did not match the expected
         value. Please verify that you have the proper URL setup and that

test/unit/vagrant/action/builtin/box_add_test.rb

@@ -209,6 +209,29 @@ describe Vagrant::Action::Builtin::BoxAdd, :skip_windows, :bsdtar do
         to raise_error(Vagrant::Errors::BoxChecksumMismatch)
     end
 
+    it "ignores checksums if empty string" do
+      box_path = iso_env.box2_file(:virtualbox)
+      with_web_server(box_path) do |port|
+        env[:box_name] = "foo"
+        env[:box_url] = "http://127.0.0.1:#{port}/#{box_path.basename}"
+        env[:box_checksum] = ""
+        env[:box_checksum_type] = ""
+
+
+        expect(box_collection).to receive(:add).with(any_args) { |path, name, version, **opts|
+          expect(checksum(path)).to eq(checksum(box_path))
+          expect(name).to eq("foo")
+          expect(version).to eq("0")
+          expect(opts[:metadata_url]).to be_nil
+          true
+        }.and_return(box)
+
+        expect(app).to receive(:call).with(env)
+
+        subject.call(env)
+      end
+    end
+
     it "does not raise an error if the checksum has different case" do
       box_path = iso_env.box2_file(:virtualbox)