diff --git a/OpenXmlFormats/Wordprocessing/wml.cs b/OpenXmlFormats/Wordprocessing/wml.cs
index fa7aa3937..77eda1fcb 100644
--- a/OpenXmlFormats/Wordprocessing/wml.cs
+++ b/OpenXmlFormats/Wordprocessing/wml.cs
@@ -2258,7 +2258,10 @@ internal void Write(StreamWriter sw, string nodeName)
             this.space = "preserve";
             XmlHelper.WriteAttribute(sw, "xml:space", this.space);
             sw.Write(">");
-            sw.Write(XmlHelper.EncodeXml(this.valueField));
+            if (this.valueField != null)
+            {
+                sw.Write(XmlHelper.EncodeXml(this.valueField));
+            }
             sw.Write(string.Format("</w:{0}>", nodeName));
         }