diff --git a/src/RhinoInside.Revit.External/DB/Extensions/BoundingBoxXYZ.cs b/src/RhinoInside.Revit.External/DB/Extensions/BoundingBoxXYZ.cs
index ec54333b8..8aed89412 100644
--- a/src/RhinoInside.Revit.External/DB/Extensions/BoundingBoxXYZ.cs
+++ b/src/RhinoInside.Revit.External/DB/Extensions/BoundingBoxXYZ.cs
@@ -252,7 +252,7 @@ public static void CopyFrom(this BoundingBoxXYZ value, BoundingBoxXYZ other)
 
     public static XYZ Evaluate(this BoundingBoxXYZ value, UnitXYZ xyz)
     {
-      if (!xyz) return default;
+      if (xyz.IsNaN) return XYZExtension.NaN;
 
       var (x, y, z) = xyz;
       var (min, max) = value;
diff --git a/src/RhinoInside.Revit.External/DB/Extensions/Curve.cs b/src/RhinoInside.Revit.External/DB/Extensions/Curve.cs
index db1a8b458..4ce7bf79f 100644
--- a/src/RhinoInside.Revit.External/DB/Extensions/Curve.cs
+++ b/src/RhinoInside.Revit.External/DB/Extensions/Curve.cs
@@ -273,7 +273,7 @@ public static bool TryGetLocation(this NurbSpline curve, out XYZ origin, out Uni
           cov.SetCovariance(ctrlPoints, plane.Project(cov.Origin));
           basisY = cov.GetPrincipalComponent(0D);
 
-          if (!basisY)
+          if (basisY.IsNaN)
             basisY = basisX.Right();
         }
       }
@@ -296,7 +296,7 @@ public static bool TryGetLocation(this NurbSpline curve, out XYZ origin, out Uni
           cov.SetCovariance(ctrlPoints.Skip(closed), plane.Project(cov.Origin));
           basisY = cov.GetPrincipalComponent(0D);
 
-          if (!basisY)
+          if (basisY.IsNaN)
             basisY = basisX.Right();
         }
       }
diff --git a/src/RhinoInside.Revit.External/DB/Extensions/ElementLocation.cs b/src/RhinoInside.Revit.External/DB/Extensions/ElementLocation.cs
index 1eb75a395..1e7946c2b 100644
--- a/src/RhinoInside.Revit.External/DB/Extensions/ElementLocation.cs
+++ b/src/RhinoInside.Revit.External/DB/Extensions/ElementLocation.cs
@@ -85,7 +85,7 @@ internal static void SetLocation<T>(this T element, XYZ newOrigin, UnitXYZ newBa
         UnitXYZ.Orthonormal(basisX, basisY, out var basisZ);
 
         newBasisX = (new PlaneEquation(origin, basisZ).Project(origin + newBasisX) - origin).ToUnitXYZ();
-        if (newBasisX && !basisX.AlmostEquals(newBasisX))
+        if (!newBasisX.IsNaN && !basisX.AlmostEquals(newBasisX))
         {
           if (element.Pinned) element.Pinned = false;
           using (var axis = Line.CreateUnbound(origin, basisZ))
diff --git a/src/RhinoInside.Revit.External/DB/Extensions/Solid.cs b/src/RhinoInside.Revit.External/DB/Extensions/Solid.cs
index 44828ef8a..8c3bf6a8d 100644
--- a/src/RhinoInside.Revit.External/DB/Extensions/Solid.cs
+++ b/src/RhinoInside.Revit.External/DB/Extensions/Solid.cs
@@ -382,7 +382,7 @@ public static IntersectionResult Project(this Edge edge, XYZ point, out Face fac
         var vector = (point - intersection.XYZPoint).ToUnitXYZ();
 
         var faces = new Face[] { edge.GetFace(0), edge.GetFace(1) };
-        if (vector)
+        if (!vector.IsNaN)
         {
           var dot0 = double.PositiveInfinity;
           if (faces[0] is object)
diff --git a/src/RhinoInside.Revit.External/DB/Extensions/Transform.cs b/src/RhinoInside.Revit.External/DB/Extensions/Transform.cs
index 79c7ebd97..3755b0d01 100644
--- a/src/RhinoInside.Revit.External/DB/Extensions/Transform.cs
+++ b/src/RhinoInside.Revit.External/DB/Extensions/Transform.cs
@@ -136,7 +136,7 @@ internal static UnitXYZ GetPrincipalComponent(this Transform covarianceMatrix, d
       var principal = covarianceMatrix.OfVector(previous).ToUnitXYZ();
 
       var iterations = 50;
-      while (--iterations > 0 && principal && !previous.AlmostEquals(principal, tolerance))
+      while (--iterations > 0 && !principal.IsNaN && !previous.AlmostEquals(principal, tolerance))
       {
         previous = principal;
         principal = covarianceMatrix.OfVector(previous).ToUnitXYZ();
diff --git a/src/RhinoInside.Revit.External/DB/Extensions/XYZ.cs b/src/RhinoInside.Revit.External/DB/Extensions/XYZ.cs
index de1b14bbe..7ba80bba9 100644
--- a/src/RhinoInside.Revit.External/DB/Extensions/XYZ.cs
+++ b/src/RhinoInside.Revit.External/DB/Extensions/XYZ.cs
@@ -9,7 +9,7 @@ namespace RhinoInside.Revit.External.DB.Extensions
 
   public static class XYZExtension
   {
-    public static XYZ NaN    { get; } = null; // new XYZ(double.NaN, double.NaN, double.NaN);
+    public static XYZ NaN    { get; } = default;
     public static XYZ Zero   { get; } = XYZ.Zero;
     public static XYZ One    { get; } = new XYZ(1.0, 1.0, 1.0);
 
@@ -104,7 +104,7 @@ public static double Norm(this XYZ xyz, double tolerance = Constant.DefaultToler
     public static UnitXYZ ToUnitXYZ(this XYZ xyz)
     {
       var (x, y, z) = xyz;
-      return Euclidean.Normalize3(ref x, ref y, ref z) ? (UnitXYZ) new XYZ(x, y, z) : default;
+      return Euclidean.Normalize3(ref x, ref y, ref z) ? (UnitXYZ) new XYZ(x, y, z) : UnitXYZ.NaN;
     }
 
     /// <summary>
diff --git a/src/RhinoInside.Revit.External/DB/UnitXYZ.cs b/src/RhinoInside.Revit.External/DB/UnitXYZ.cs
index 1e7dd0a82..e37fe7c98 100644
--- a/src/RhinoInside.Revit.External/DB/UnitXYZ.cs
+++ b/src/RhinoInside.Revit.External/DB/UnitXYZ.cs
@@ -22,7 +22,7 @@ public readonly struct UnitXYZ
     public static UnitXYZ BasisY { get; } = new UnitXYZ(XYZ.BasisY);
     public static UnitXYZ BasisZ { get; } = new UnitXYZ(XYZ.BasisZ);
 
-    public static implicit operator bool(UnitXYZ unit) => unit.Direction is object;
+    public bool IsNaN => Direction is null;
     public static XYZ operator *(UnitXYZ unit, double magnitude) => unit.Direction * magnitude;
     public static XYZ operator *(double magnitude, UnitXYZ unit) => magnitude * unit.Direction;
 
@@ -105,7 +105,7 @@ public static bool Orthonormalize(XYZ u, XYZ v, out UnitXYZ x, out UnitXYZ y, ou
       x = u.ToUnitXYZ();
       y = v.ToUnitXYZ();
       z = CrossProduct(x, y).ToUnitXYZ();
-      if (!z) return false;
+      if (z.IsNaN) return false;
 
       y = (UnitXYZ) CrossProduct(z, x);
       return true;