failed to build navmesh in unity3d

src/DotRecast.Recast.Demo/RecastDemo.cs

@@ -687,6 +687,12 @@ public class RecastDemo : IRecastDemoChannel
             buildResult = soloNavMeshBuilder.Build(_sample.GetInputGeom(), settings);
         }
 
+        if (!buildResult.Success)
+        {
+            Logger.Error("failed to build");
+            return;
+        }
+
         _sample.Update(_sample.GetInputGeom(), buildResult.RecastBuilderResults, buildResult.NavMesh);
         _sample.SetChanged(false);
         settingsView.SetBuildTime((RcFrequency.Ticks - t) / TimeSpan.TicksPerMillisecond);

src/DotRecast.Recast.DemoTool/Builder/NavMeshBuildResult.cs

@@ -1,15 +1,25 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using DotRecast.Detour;
 
 namespace DotRecast.Recast.DemoTool.Builder
 {
     public class NavMeshBuildResult
     {
+        public readonly bool Success;
         public readonly IList<RecastBuilderResult> RecastBuilderResults;
         public readonly DtNavMesh NavMesh;
 
+        public NavMeshBuildResult()
+        {
+            Success = false;
+            RecastBuilderResults = Array.Empty<RecastBuilderResult>();
+            NavMesh = null;
+        }
+        
         public NavMeshBuildResult(IList<RecastBuilderResult> recastBuilderResults, DtNavMesh navMesh)
         {
+            Success = true;
             RecastBuilderResults = recastBuilderResults;
             NavMesh = navMesh;
         }

src/DotRecast.Recast.DemoTool/Builder/SoloNavMeshBuilder.cs

@@ -49,6 +49,11 @@ namespace DotRecast.Recast.DemoTool.Builder
                 filterWalkableLowHeightSpans);
 
             var meshData = BuildMeshData(geom, cellSize, cellHeight, agentHeight, agentRadius, agentMaxClimb, rcResult);
+            if (null == meshData)
+            {
+                return new NavMeshBuildResult();
+            }
+
             var navMesh = BuildNavMesh(meshData, vertsPerPoly);
             return new NavMeshBuildResult(ImmutableArray.Create(rcResult), navMesh);
         }
@@ -79,6 +84,11 @@ namespace DotRecast.Recast.DemoTool.Builder
             DtNavMeshCreateParams option = DemoNavMeshBuilder
                 .GetNavMeshCreateParams(geom, cellSize, cellHeight, agentHeight, agentRadius, agentMaxClimb, result);
             var meshData = NavMeshBuilder.CreateNavMeshData(option);
+            if (null == meshData)
+            {
+                return null;
+            }
+
             return DemoNavMeshBuilder.UpdateAreaAndFlags(meshData);
         }
     }