(cake-buildGH-2474) Refactor TeamCityProvider.BuildProblem method for…

… API consistency

This change will suppress the "identity" token if the value provided is null or empty.
This directory resolves the issue of the provider attempting to sanitize a null reference
on a value that, per Jetbrains documentation, is not required for the buildProblem
service message

src/Cake.Common.Tests/Unit/Build/TeamCity/TeamCityProviderTests.cs

@@ -128,5 +128,26 @@ public void SetParameter_Should_Write_To_The_Log_Correctly()
                     fixture.Log.AggregateLogMessages());
             }
         }
+
+        public sealed class TheBuildProblemMethod
+        {
+            [Theory]
+            [InlineData("A build problem", "identity_id", "description='A build problem' identity='identity_id'")]
+            [InlineData("A build problem", "", "description='A build problem'")]
+            [InlineData("A build problem", null, "description='A build problem'")]
+            public void BuildProblem_Should_Write_To_The_Log_Correctly(string description, string identity, string expected)
+            {
+                // Given
+                var fixture = new TeamCityFixture();
+                var teamCity = fixture.CreateTeamCityService();
+
+                // When
+                teamCity.BuildProblem(description, identity);
+
+                // Then
+                Assert.Equal($"##teamcity[buildProblem {expected}]" + Environment.NewLine,
+                    fixture.Log.AggregateLogMessages());
+            }
+        }
     }
 }

src/Cake.Common/Build/TeamCity/TeamCityProvider.cs

@@ -263,11 +263,13 @@ public void ImportDotCoverCoverage(FilePath snapshotFile, DirectoryPath dotCover
         /// <param name="identity">Build identity.</param>
         public void BuildProblem(string description, string identity)
         {
-            WriteServiceMessage("buildProblem", new Dictionary<string, string>
+            var tokens = new Dictionary<string, string> { { "description", description } };
+            if (!string.IsNullOrEmpty(identity))
             {
-                { "description", description },
-                { "identity", identity }
-            });
+                tokens.Add("identity", identity);
+            }
+
+            WriteServiceMessage("buildProblem", tokens);
         }
 
         /// <summary>