Fixed NullReferenceException when the text is null

QuestPDF.Examples/TextExamples.cs

@@ -339,5 +339,37 @@ namespace QuestPDF.Examples
                     });
                 });
         }
+        
+        [Test]
+        public void DrawingNullTextShouldNotThrowException()
+        {
+            RenderingTest
+                .Create()
+                .ProduceImages()
+                .ShowResults()
+                .RenderDocument(container =>
+                {
+                    container.Page(page =>
+                    {
+                        page.Margin(50);
+                        page.PageColor(Colors.White);
+
+                        page.Size(PageSizes.A4);
+
+                        page.Content().Column(column =>
+                        {
+                            column.Item().Text(null);
+
+                            column.Item().Text(text =>
+                            {
+                                text.Span(null);
+                                text.Line(null);
+                                text.Hyperlink(null, "http://www.questpdf.com");
+                                text.TotalPages().Format(x => null);
+                            });
+                        });
+                    });
+                });
+        }
     }
 }

QuestPDF/Elements/Text/Items/TextBlockPageNumber.cs

@@ -11,19 +11,19 @@ namespace QuestPDF.Elements.Text.Items
         
         public override TextMeasurementResult? Measure(TextMeasurementRequest request)
         {
-            SetPageNumber(request.PageContext);
+            UpdatePageNumberText(request.PageContext);
             return MeasureWithoutCache(request);
         }
 
         public override void Draw(TextDrawingRequest request)
         {
-            SetPageNumber(request.PageContext);
+            UpdatePageNumberText(request.PageContext);
             base.Draw(request);
         }
 
-        private void SetPageNumber(IPageContext context)
+        private void UpdatePageNumberText(IPageContext context)
         {
-            Text = Source(context) ?? PageNumberPlaceholder;
+            Text = Source(context) ?? string.Empty;
         }
     }
 }

QuestPDF/Fluent/TextExtensions.cs

@@ -24,7 +24,7 @@ namespace QuestPDF.Fluent
     
     public class TextPageNumberDescriptor : TextSpanDescriptor
     {
-        internal PageNumberFormatter FormatFunction { get; private set; } = x => (x ?? 123).ToString();
+        internal PageNumberFormatter FormatFunction { get; private set; } = x => x?.ToString() ?? string.Empty;
 
         internal TextPageNumberDescriptor(TextStyle textStyle) : base(textStyle)
         {
@@ -92,6 +92,10 @@ namespace QuestPDF.Fluent
         public TextSpanDescriptor Span(string? text)
         {
             var style = DefaultStyle.Clone();
+            var descriptor = new TextSpanDescriptor(style);
+
+            if (text == null)
+                return descriptor;
  
             var items = text
                 .Replace("\r", string.Empty)
@@ -114,7 +118,7 @@ namespace QuestPDF.Fluent
                 .ToList()
                 .ForEach(TextBlocks.Add);
 
-            return new TextSpanDescriptor(style);
+            return descriptor;
         }
 
         public TextSpanDescriptor Line(string? text)