Don't try to recover machine without a uuid

lib/vagrant/machine_index.rb

@@ -263,7 +263,7 @@ module Vagrant
     #
     # @return [Hash]
     def find_by_prefix(prefix)
-      return nil if prefix.nil?
+      return if !prefix
       @machines.each do |uuid, data|
         return data.merge("id" => uuid) if uuid.start_with?(prefix)
       end

lib/vagrant/plugin/v2/command.rb

@@ -230,7 +230,8 @@ module Vagrant
           color_index = 0
 
           machines.each do |machine|
-            if machine.state && machine.state.id != :not_created && !@env.machine_index.include?(machine.index_uuid)
+            if (machine.state && machine.state.id != :not_created && 
+                !machine.index_uuid.nil? && !@env.machine_index.include?(machine.index_uuid))
               machine.recover_machine(machine.state.id)
             end
 

test/unit/vagrant/plugin/v2/command_test.rb

@@ -1,5 +1,6 @@
 require File.expand_path("../../../../base", __FILE__)
 require 'optparse'
+require 'vagrant/machine_index'
 
 describe Vagrant::Plugin::V2::Command do
   include_context "unit"
@@ -151,6 +152,40 @@ describe Vagrant::Plugin::V2::Command do
       instance.with_target_vms("foo") { |vm| vms << vm }
     end
 
+    it "does not recover the vm if it has no uuid" do
+      foo_vm = double("foo")
+      provider = :foobarbaz
+      state_id = :some_state
+      allow(foo_vm).to receive(:name).and_return("foo")
+      allow(foo_vm).to receive(:provider).and_return(provider)
+      allow(foo_vm).to receive(:ui).and_return(Vagrant::UI::Silent.new)
+      allow(foo_vm).to receive(:state).and_return(double("state", id: state_id))
+      allow(foo_vm).to receive(:index_uuid).and_return(nil)
+      allow(environment).to receive(:machine).with(:foo, provider).and_return(foo_vm)
+      
+      expect(foo_vm).not_to receive(:recover_machine).with(state_id)
+      vms = []
+      instance.with_target_vms("foo", provider: provider) { |vm| vms << vm }
+      expect(vms).to eq([foo_vm])
+    end
+
+    it "recovers the vm" do
+      foo_vm = double("foo")
+      provider = :foobarbaz
+      state_id = :some_state
+      allow(foo_vm).to receive(:name).and_return("foo")
+      allow(foo_vm).to receive(:provider).and_return(provider)
+      allow(foo_vm).to receive(:ui).and_return(Vagrant::UI::Silent.new)
+      allow(foo_vm).to receive(:state).and_return(double("state", id: state_id))
+      allow(foo_vm).to receive(:index_uuid).and_return("someuuid")
+      allow(environment).to receive(:machine).with(:foo, provider).and_return(foo_vm)
+      
+      expect(foo_vm).to receive(:recover_machine).with(state_id)
+      vms = []
+      instance.with_target_vms("foo", provider: provider) { |vm| vms << vm }
+      expect(vms).to eq([foo_vm])
+    end
+
     it "yields the given VM with proper provider if given" do
       foo_vm = double("foo")
       provider = :foobarbaz