fixed coalesce macro behavior

Author: vlada-shubina

src/Microsoft.TemplateEngine.Orchestrator.RunnableProjects/Macros/CoalesceMacro.cs

@@ -19,22 +19,23 @@ public override void Evaluate(IEngineEnvironmentSettings environmentSettings, IV
         {
             if (variableCollection.TryGetValue(config.SourceVariableName, out object currentSourceValue) && currentSourceValue != null)
             {
-                variableCollection[config.VariableName] = currentSourceValue;
-                environmentSettings.Host.Logger.LogDebug("[{macro}]: Assigned variable '{var}' to '{value}'.", nameof(CoalesceMacro), config.VariableName, currentSourceValue);
-                return;
+                if (config.DefaultValue != null && currentSourceValue.Equals(config.DefaultValue))
+                {
+                    environmentSettings.Host.Logger.LogDebug("[{macro}]: '{var}': source value '{source}' is not used, because it is equal to default value '{default}'.", nameof(CoalesceMacro), config.VariableName, currentSourceValue, config.DefaultValue);
+                }
+                else
+                {
+                    variableCollection[config.VariableName] = currentSourceValue;
+                    environmentSettings.Host.Logger.LogDebug("[{macro}]: Assigned variable '{var}' to '{value}'.", nameof(CoalesceMacro), config.VariableName, currentSourceValue);
+                    return;
+                }
             }
             if (variableCollection.TryGetValue(config.FallbackVariableName, out object currentFallbackValue) && currentFallbackValue != null)
             {
                 variableCollection[config.VariableName] = currentFallbackValue;
                 environmentSettings.Host.Logger.LogDebug("[{macro}]: Assigned variable '{var}' to fallback value '{value}'.", nameof(CoalesceMacro), config.VariableName, currentFallbackValue);
                 return;
             }
-            else if (config.DefaultValue != null)
-            {
-                variableCollection[config.VariableName] = config.DefaultValue;
-                environmentSettings.Host.Logger.LogDebug("[{macro}]: Assigned variable '{var}' to default value '{value}'.", nameof(CoalesceMacro), config.VariableName, config.DefaultValue);
-                return;
-            }
             environmentSettings.Host.Logger.LogDebug("[{macro}]: Variable '{var}' was not assigned, neither source nor fallback variable was found.", nameof(CoalesceMacro), config.VariableName);
         }