Check if CurrentSubpath is null in CloseSubpath()

src/UglyToad.PdfPig.Tests/Graphics/TestOperationContext.cs

@@ -66,7 +66,7 @@
         {
         }
 
-        public PdfPoint CloseSubpath()
+        public PdfPoint? CloseSubpath()
         {
             return new PdfPoint();
         }

src/UglyToad.PdfPig/Graphics/ContentStreamProcessor.cs

@@ -419,8 +419,13 @@
             CurrentSubpath = new PdfSubpath();
         }
 
-        public PdfPoint CloseSubpath()
+        public PdfPoint? CloseSubpath()
         {
+            if (CurrentSubpath == null)
+            {
+                return null;
+            }
+
             PdfPoint point;
             if (CurrentSubpath.Commands[0] is Move move)
             {

src/UglyToad.PdfPig/Graphics/IOperationContext.cs

@@ -89,7 +89,7 @@
         /// <summary>
         /// Close the current subpath.
         /// </summary>
-        PdfPoint CloseSubpath();
+        PdfPoint? CloseSubpath();
 
         /// <summary>
         /// Add the current subpath to the path.

src/UglyToad.PdfPig/Graphics/Operations/PathConstruction/CloseSubpath.cs

@@ -29,7 +29,11 @@
         /// <inheritdoc />
         public void Run(IOperationContext operationContext)
         {
-            operationContext.CurrentPosition = operationContext.CloseSubpath();
+            var point = operationContext.CloseSubpath();
+            if (point.HasValue)
+            {
+                operationContext.CurrentPosition = point.Value;
+            }
         }
 
         /// <inheritdoc />