Fix nested table breaking the Word validation #190

Author: onizet

src/Html2OpenXml/Expressions/Table/TableCellExpression.cs

@@ -31,9 +31,6 @@ public override IEnumerable<OpenXmlElement> Interpret (ParsingContext context)
     {
         var childElements = base.Interpret (context);
 
-        if (!childElements.Any()) // Word requires that the cell is not empty
-            childElements = [new Paragraph()];
-
         var cell = new TableCell (cellProperties);
 
         if (cellNode.ColumnSpan > 1)
@@ -46,6 +43,13 @@ public override IEnumerable<OpenXmlElement> Interpret (ParsingContext context)
             cellProperties.VerticalMerge = new() { Val = MergedCellValues.Restart };
         }
 
+        // Word requires at least one paragraph in a cell
+        // OpenXmlValidator does not catch this error
+        if (!childElements.OfType<Paragraph>().Any())
+        {
+            childElements = childElements.Append(new Paragraph());
+        }
+
         cell.Append(childElements);
         return [cell];
     }

test/HtmlToOpenXml.Tests/TableTests.cs

@@ -493,6 +493,7 @@ public void NestedTable_ReturnsTableInsideTable()
             var cell = elements[0].GetFirstChild<TableRow>()?.GetFirstChild<TableCell>();
             Assert.That(cell, Is.Not.Null);
             Assert.That(cell.HasChild<Table>(), Is.True);
+            Assert.That(cell.HasChild<Paragraph>(), Is.True, "Word requires at least a paragraph");
         }
 
         [Test]