Azure.Provisioning: Avoid excess nulls in BicepStringBuilder (#46742)

Author: tg-msft

sdk/provisioning/Azure.Provisioning.Storage/tests/BasicStorageTests.cs

@@ -270,11 +270,12 @@ await test.Define(
                 infra.Add(new ProvisioningOutput("blobs_endpoint", typeof(string)) { Value = storage.PrimaryEndpoints.Value!.BlobUri });
 
                 // Manually compute the public Azure endpoint
+                string? nothing = null;
                 BicepValue<string> computed =
                     new BicepStringBuilder()
                     .Append("https://")
                     .Append($"{storage.Name}")
-                    .Append(".blob.core.windows.net");
+                    .Append($".blob.core.windows.net{nothing}");
                 infra.Add(new ProvisioningOutput("computed_endpoint", typeof(string)) { Value = computed });
 
                 return infra;

sdk/provisioning/Azure.Provisioning/src/Expressions/BicepStringBuilder.cs

@@ -102,10 +102,11 @@ public void AppendFormatted<T>(T t)
         }
         else
         {
-            _expressions.Add(
-                t is null ?
-                    BicepSyntax.Null() :
-                    BicepSyntax.Value(t.ToString() ?? ""));
+            string? s = t?.ToString();
+            if (s is not null)
+            {
+                _expressions.Add(BicepSyntax.Value(s));
+            }
         }
     }