feat: add additional null checks to implicit conversions

When clients have <Nullable> turned off, the C# compiler won't hint that null shouldn't be passed as the errors array/list. By explicitly checking for null, we eliminate these error cases.

Signed-off-by: Kenny Pflug <kenny.pflug@live.de>

src/ErrorOr/ErrorOr.ImplicitConverters.cs

@@ -1,46 +1,56 @@
-namespace ErrorOr;
-
-public readonly partial record struct ErrorOr<TValue> : IErrorOr<TValue>
-{
-    /// <summary>
-    /// Creates an <see cref="ErrorOr{TValue}"/> from a value.
-    /// </summary>
-    public static implicit operator ErrorOr<TValue>(TValue value)
-    {
-        return new ErrorOr<TValue>(value);
-    }
-
-    /// <summary>
-    /// Creates an <see cref="ErrorOr{TValue}"/> from an error.
-    /// </summary>
-    public static implicit operator ErrorOr<TValue>(Error error)
-    {
-        return new ErrorOr<TValue>(error);
-    }
-
-    /// <summary>
-    /// Creates an <see cref="ErrorOr{TValue}"/> from a list of errors.
-    /// </summary>
-    public static implicit operator ErrorOr<TValue>(List<Error> errors)
-    {
-        if (errors.Count == 0)
-        {
-            throw new InvalidOperationException("Cannot create an ErrorOr<TValue> from an empty list of errors. Provide at least one error.");
-        }
-
-        return new ErrorOr<TValue>(errors);
-    }
-
-    /// <summary>
-    /// Creates an <see cref="ErrorOr{TValue}"/> from a list of errors.
-    /// </summary>
-    public static implicit operator ErrorOr<TValue>(Error[] errors)
-    {
-        if (errors.Length == 0)
-        {
-            throw new InvalidOperationException("Cannot create an ErrorOr<TValue> from an empty array of errors. Provide at least one error.");
-        }
-
-        return new ErrorOr<TValue>(errors.ToList());
-    }
-}
+namespace ErrorOr;
+
+public readonly partial record struct ErrorOr<TValue> : IErrorOr<TValue>
+{
+    /// <summary>
+    /// Creates an <see cref="ErrorOr{TValue}"/> from a value.
+    /// </summary>
+    public static implicit operator ErrorOr<TValue>(TValue value)
+    {
+        return new ErrorOr<TValue>(value);
+    }
+
+    /// <summary>
+    /// Creates an <see cref="ErrorOr{TValue}"/> from an error.
+    /// </summary>
+    public static implicit operator ErrorOr<TValue>(Error error)
+    {
+        return new ErrorOr<TValue>(error);
+    }
+
+    /// <summary>
+    /// Creates an <see cref="ErrorOr{TValue}"/> from a list of errors.
+    /// </summary>
+    public static implicit operator ErrorOr<TValue>(List<Error> errors)
+    {
+        if (errors is null)
+        {
+            throw new ArgumentNullException(nameof(errors));
+        }
+
+        if (errors.Count == 0)
+        {
+            throw new InvalidOperationException("Cannot create an ErrorOr<TValue> from an empty list of errors. Provide at least one error.");
+        }
+
+        return new ErrorOr<TValue>(errors);
+    }
+
+    /// <summary>
+    /// Creates an <see cref="ErrorOr{TValue}"/> from a list of errors.
+    /// </summary>
+    public static implicit operator ErrorOr<TValue>(Error[] errors)
+    {
+        if (errors is null)
+        {
+            throw new ArgumentNullException(nameof(errors));
+        }
+
+        if (errors.Length == 0)
+        {
+            throw new InvalidOperationException("Cannot create an ErrorOr<TValue> from an empty array of errors. Provide at least one error.");
+        }
+
+        return new ErrorOr<TValue>(errors.ToList());
+    }
+}

tests/ErrorOr/ErrorOr.InstantiationTests.cs

@@ -376,4 +376,22 @@ public void CreateErrorOr_WhenEmptyErrorsArray_ShouldThrow()
         // Assert
         errorOrInt.Should().ThrowExactly<InvalidOperationException>();
     }
+
+    [Fact]
+    public void CreateErrorOr_WhenNullIsPassedAsErrorsList_ShouldThrowArgumentNullException()
+    {
+        Func<ErrorOr<int>> act = () => default(List<Error>)!;
+
+        act.Should().ThrowExactly<ArgumentNullException>()
+           .And.ParamName.Should().Be("errors");
+    }
+
+    [Fact]
+    public void CreateErrorOr_WhenNullIsPassedAsErrorsArray_ShouldThrowArgumentNullException()
+    {
+        Func<ErrorOr<int>> act = () => default(Error[])!;
+
+        act.Should().ThrowExactly<ArgumentNullException>()
+           .And.ParamName.Should().Be("errors");
+    }
 }