Better handling of NaN in nullable numeric assertions

Src/FluentAssertions/AssertionExtensions.cs

@@ -686,7 +686,7 @@ public static NumericAssertions<float> Should(this float actualValue)
         [Pure]
         public static NullableNumericAssertions<float> Should(this float? actualValue)
         {
-            return new NullableNumericAssertions<float>(actualValue);
+            return new NullableFloatAssertions(actualValue);
         }
 
         /// <summary>
@@ -706,7 +706,7 @@ public static NumericAssertions<double> Should(this double actualValue)
         [Pure]
         public static NullableNumericAssertions<double> Should(this double? actualValue)
         {
-            return new NullableNumericAssertions<double>(actualValue);
+            return new NullableDoubleAssertions(actualValue);
         }
 
         /// <summary>

Src/FluentAssertions/Numeric/NullableDoubleAssertions.cs

@@ -0,0 +1,12 @@
+namespace FluentAssertions.Numeric
+{
+    internal class NullableDoubleAssertions : NullableNumericAssertions<double>
+    {
+        public NullableDoubleAssertions(double? value)
+            : base(value)
+        {
+        }
+
+        private protected override bool IsNaN(double value) => double.IsNaN(value);
+    }
+}

Src/FluentAssertions/Numeric/NullableFloatAssertions.cs

@@ -0,0 +1,12 @@
+namespace FluentAssertions.Numeric
+{
+    internal class NullableFloatAssertions : NullableNumericAssertions<float>
+    {
+        public NullableFloatAssertions(float? value)
+            : base(value)
+        {
+        }
+
+        private protected override bool IsNaN(float value) => float.IsNaN(value);
+    }
+}