Check subject for null

Src/FluentAssertions/Primitives/ReferenceTypeAssertions.cs

@@ -432,9 +432,13 @@ public AndConstraint<TAssertions> Satisfy<T>(Action<T> assertion)
  Guard.ThrowIfArgumentIsNull(assertion, nameof(assertion), "Cannot verify an object against a <null> inspector.");
 
  Execute.Assertion
+ .ForCondition(Subject is not null)
+ .WithDefaultIdentifier(Identifier)
+ .FailWith("Expected {context:object} to be assignable to {0}{reason}, but found <null>.", typeof(T))
+ .Then
  .ForCondition(Subject is T)
  .WithDefaultIdentifier(Identifier)
- .FailWith("Expected {context:object} to be assignable to {0}{reason}, but {1} is not.", typeof(T), Subject.GetType());
+ .FailWith("Expected {context:object} to be assignable to {0}{reason}, but {1} is not.", typeof(T), Subject!.GetType());
 
  string[] failuresFromInspector;
 

Tests/FluentAssertions.Specs/Primitives/ReferenceTypeAssertionsSpecs.Satisfy.cs

@@ -244,6 +244,31 @@ public void Base_class_satisfied_against_sub_class_throws()
  $"Expected {nameof(baseClass)} to be assignable to {typeof(SubClass)}, but {typeof(BaseClass)} is not.");
  }
 
+ [Fact]
+ public void Nested_assertion_on_null_throws()
+ {
+ // Arrange
+ var complexDto = new PersonAndAddressDto
+ {
+ Person = new PersonDto
+ {
+ Name = "Buford Howard Tannen",
+ },
+ Address = null,
+ };
+
+ // Act
+ Action act = () => complexDto.Should().Satisfy<PersonAndAddressDto>(dto =>
+ {
+ dto.Person.Name.Should().Be("Buford Howard Tannen");
+ dto.Address.Should().Satisfy<AddressDto>(address => address.City.Should().Be("Hill Valley"));
+ });
+
+ // Assert
+ act.Should().Throw<XunitException>()
+ .WithMessage("Expected dto.Address to be assignable to *AddressDto, but found <null>.");
+ }
+
  private class PersonDto
  {
  public string Name { get; init; }