From 39c0135f90f7a51729c3857e3ddd4e10ca4c5c94 Mon Sep 17 00:00:00 2001
From: Andriy Svyryd <Andriy.Svyryd@microsoft.com>
Date: Tue, 2 Nov 2021 18:10:52 -0700
Subject: [PATCH] Avoid NRE in ForeignKeyAttributeConvention

Fixes #26436
---
 .../ForeignKeyAttributeConvention.cs          |  2 +-
 .../DataAnnotationTestBase.cs                 | 39 +++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/src/EFCore/Metadata/Conventions/ForeignKeyAttributeConvention.cs b/src/EFCore/Metadata/Conventions/ForeignKeyAttributeConvention.cs
index 6694cc571e6..fe14c220124 100644
--- a/src/EFCore/Metadata/Conventions/ForeignKeyAttributeConvention.cs
+++ b/src/EFCore/Metadata/Conventions/ForeignKeyAttributeConvention.cs
@@ -345,7 +345,7 @@ var fkPropertiesOnDependentToPrincipal
                 }
             }
 
-            return newRelationshipBuilder.HasForeignKey(fkPropertiesToSet, fromDataAnnotation: true);
+            return newRelationshipBuilder?.HasForeignKey(fkPropertiesToSet, fromDataAnnotation: true);
         }
 
         private static IConventionForeignKeyBuilder? SplitNavigationsToSeparateRelationships(
diff --git a/test/EFCore.Specification.Tests/DataAnnotationTestBase.cs b/test/EFCore.Specification.Tests/DataAnnotationTestBase.cs
index c7ebab2e2e6..078c8dd12d7 100644
--- a/test/EFCore.Specification.Tests/DataAnnotationTestBase.cs
+++ b/test/EFCore.Specification.Tests/DataAnnotationTestBase.cs
@@ -1105,6 +1105,45 @@ protected class Profile4
             public virtual Login4 User { get; set; }
         }
 
+        [ConditionalFact]
+        public virtual void Required_and_ForeignKey_to_ForeignKey_can_be_overridden()
+        {
+            var modelBuilder = CreateModelBuilder();
+
+            modelBuilder.Entity<Login3>()
+                .HasOne(p => p.Profile)
+                .WithOne(p => p.User)
+                .HasForeignKey<Login3>("ProfileId");
+
+            var model = Validate(modelBuilder);
+
+            var loginFk = GetProperty<Login3>(model, "ProfileId").GetContainingForeignKeys().Single();
+            Assert.True(loginFk.IsRequired); // This will be False after #15898 is fixed
+            Assert.True(loginFk.IsRequiredDependent);
+
+            Assert.False(GetProperty<Profile3>(model, nameof(Profile3.Profile3Id)).IsForeignKey());
+        }
+
+        [Table("Employee")]
+        public class Employee1
+        {
+            [Key]
+            [Column("EmployeeId")]
+            public decimal EmployeeId { get; set; }
+
+            [ForeignKey("EmployeeId")]
+            public EmployeeDetail EmployeeDetail { get; set; }
+        }
+
+        [Table("EmployeeDetail")]
+        public class EmployeeDetail
+        {
+            [Key]
+            public decimal EmployeeId { get; set; }
+
+            public Employee1 Employee { get; set; }
+        }
+
         [ConditionalFact]
         public virtual void ForeignKey_to_nothing()
         {