#500 validate that there is an address in consul service, also made this clear in docs (#520)

docs/features/servicediscovery.rst

@@ -63,7 +63,7 @@ You services need to be added to Consul something like below (c# style but hopef
 is not to add http or https to the Address field. I have been contacted before about not accepting scheme in Address and accepting scheme
 in address. After reading `this <https://www.consul.io/docs/agent/services.html>`_ I don't think the scheme should be in there.
 
-.. code-block: json
+.. code-block: csharp
 
     new AgentService()
     {
@@ -73,6 +73,17 @@ in address. After reading `this <https://www.consul.io/docs/agent/services.html>
         ID = "some-id",
     }
 
+Or 
+
+.. code-block:: json
+
+     "Service": {
+            "ID": "some-id",
+            "Service": "some-service-name",
+            "Address": "localhost",
+            "Port": 8080
+        }
+
 ACL Token
 ---------
 

src/Ocelot/ServiceDiscovery/Errors/UnableToFindServiceDiscoveryProviderError.cs

@@ -1,12 +0,0 @@
-using Ocelot.Errors;
-
-namespace Ocelot.ServiceDiscovery.Errors
-{
-    public class UnableToFindServiceDiscoveryProviderError : Error
-    {
-        public UnableToFindServiceDiscoveryProviderError(string message) 
-            : base(message, OcelotErrorCode.UnableToFindServiceDiscoveryProviderError)
-        {
-        }
-    }
-}

src/Ocelot/ServiceDiscovery/Providers/ConsulServiceDiscoveryProvider.cs

@@ -59,7 +59,7 @@ namespace Ocelot.ServiceDiscovery.Providers
 
         private bool IsValid(ServiceEntry serviceEntry)
         {
-            if (serviceEntry.Service.Address.Contains("http://") || serviceEntry.Service.Address.Contains("https://") || serviceEntry.Service.Port <= 0)
+            if (string.IsNullOrEmpty(serviceEntry.Service.Address) || serviceEntry.Service.Address.Contains("http://") || serviceEntry.Service.Address.Contains("https://") || serviceEntry.Service.Port <= 0)
             {
                 return false;
             }

test/Ocelot.UnitTests/ServiceDiscovery/ConsulServiceDiscoveryProviderTests.cs

@@ -31,7 +31,7 @@ namespace Ocelot.UnitTests.ServiceDiscovery
         private readonly Mock<IOcelotLoggerFactory> _factory;
         private readonly Mock<IOcelotLogger> _logger;
         private string _receivedToken;
-        private IConsulClientFactory _clientFactory;
+        private readonly IConsulClientFactory _clientFactory;
 
         public ConsulServiceDiscoveryProviderTests()
         {
@@ -134,6 +134,41 @@ namespace Ocelot.UnitTests.ServiceDiscovery
                 .BDDfy();
         }
 
+        [Fact]
+        public void should_not_return_services_with_empty_address()
+        {
+            var serviceEntryOne = new ServiceEntry()
+            {
+                Service = new AgentService()
+                {
+                    Service = _serviceName,
+                    Address = "",
+                    Port = 50881,
+                    ID = Guid.NewGuid().ToString(),
+                    Tags = new string[0]
+                },
+            };
+
+            var serviceEntryTwo = new ServiceEntry()
+            {
+                Service = new AgentService()
+                {
+                    Service = _serviceName,
+                    Address = null,
+                    Port = 50888,
+                    ID = Guid.NewGuid().ToString(),
+                    Tags = new string[0]
+                },
+            };
+
+            this.Given(x => GivenThereIsAFakeConsulServiceDiscoveryProvider(_fakeConsulServiceDiscoveryUrl, _serviceName))
+                .And(x => GivenTheServicesAreRegisteredWithConsul(serviceEntryOne, serviceEntryTwo))
+                .When(x => WhenIGetTheServices())
+                .Then(x => ThenTheCountIs(0))
+                .And(x => ThenTheLoggerHasBeenCalledCorrectlyForEmptyAddress())
+                .BDDfy();
+        }
+
         [Fact]
         public void should_not_return_services_with_invalid_port()
         {
@@ -182,6 +217,19 @@ namespace Ocelot.UnitTests.ServiceDiscovery
                 Times.Once);
         }
 
+        private void ThenTheLoggerHasBeenCalledCorrectlyForEmptyAddress()
+        {
+            _logger.Verify(
+                x => x.LogWarning(
+                    "Unable to use service Address:  and Port: 50881 as it is invalid. Address must contain host only e.g. localhost and port must be greater than 0"),
+                Times.Once);
+
+            _logger.Verify(
+                x => x.LogWarning(
+                    "Unable to use service Address:  and Port: 50888 as it is invalid. Address must contain host only e.g. localhost and port must be greater than 0"),
+                Times.Once);
+        }
+
         private void ThenTheLoggerHasBeenCalledCorrectlyForInvalidPorts()
         {
             _logger.Verify(