[release/10.0] Fix NullReferenceException when scaffolding named default constraints

.gitignore

@@ -344,3 +344,4 @@ ASALocalRun/
 
 # Local History for Visual Studio
 .localhistory/
+full.targets.txt

src/EFCore.SqlServer/Design/Internal/SqlServerAnnotationCodeGenerator.cs

@@ -233,17 +233,16 @@ public override IReadOnlyList<MethodCallCodeFragment> GenerateFluentApiCalls(
                         defaultValueAnnotation.Value,
                         defaultConstraintNameAnnotation.Value));
             }
-            else
+            else if (defaultValueSqlAnnotation != null)
             {
-                Check.DebugAssert(
-                    defaultValueSqlAnnotation != null,
-                    $"Default constraint name was set for {property.Name}, but DefaultValue and DefaultValueSql are both null.");
                 fragments.Add(
                     new MethodCallCodeFragment(
                         nameof(SqlServerPropertyBuilderExtensions.HasDefaultValueSql),
                         defaultValueSqlAnnotation.Value,
                         defaultConstraintNameAnnotation.Value));
             }
+            // If neither DefaultValue nor DefaultValueSql annotation exists (e.g., they were already removed
+            // because the default value equals the CLR default), skip generating code for the constraint name
         }
 
         var isPrimitiveCollection = property.IsPrimitiveCollection;

test/EFCore.SqlServer.Tests/Design/Internal/SqlServerAnnotationCodeGeneratorTest.cs

@@ -364,6 +364,33 @@ public void GenerateFluentApi_IProperty_works_with_IsSparse()
         }
     }
 
+    [ConditionalFact]
+    public void GenerateFluentApi_IProperty_with_DefaultConstraintName_and_no_DefaultValue_does_not_throw()
+    {
+        // Reproduces https://github.com/dotnet/efcore/issues/37175
+        // When a property has a named default constraint but no DefaultValue or DefaultValueSql annotation,
+        // GenerateFluentApiCalls should not throw a NullReferenceException
+        var generator = CreateGenerator();
+        var modelBuilder = SqlServerConventionSetBuilder.CreateModelBuilder();
+        modelBuilder.Entity("Post", x => x.Property<int>("Id"));
+        var property = modelBuilder.Model.FindEntityType("Post")!.FindProperty("Id")!;
+
+        // Create annotations dictionary with only DefaultConstraintName (simulating the scenario where
+        // DefaultValue was already removed but DefaultConstraintName wasn't)
+        var constraintNameAnnotation = RelationalAnnotationNames.DefaultConstraintName;
+        var annotations = new Dictionary<string, IAnnotation>
+        {
+            { constraintNameAnnotation, new Annotation(constraintNameAnnotation, "DF_Post_Id") }
+        };
+
+        // This should not throw - it should simply skip generating code for the constraint name
+        // since there's no default value to associate with it
+        var result = generator.GenerateFluentApiCalls((IProperty)property, annotations);
+
+        // No method calls should be generated for the constraint name alone
+        Assert.Empty(result);
+    }
+
     [ConditionalFact]
     public void GenerateFluentApi_IModel_works_with_DatabaseMaxSize()
     {