Added regex that ensures null valued properties are not omitted

Author: Microsoft Graph DevX Tooling

src/readme.graph.md

@@ -335,6 +335,11 @@ directive:
         let dateTimeToJsonRegex = /(\.Json\.JsonString\()(.*)\?(\.ToString\(@"yyyy'-'MM'-'dd'T'HH':'mm':'ss\.fffffffK")/gm
         $ = $.replace(dateTimeToJsonRegex, '$1System.DateTime.SpecifyKind($2.Value.ToUniversalTime(), System.DateTimeKind.Utc)$3');
 
+        // Enables null valued properties
+        $ = $.replace(/AddIf\(\s*null\s*!=\s*(this\._\w+)\s*\?\s*\(\s*Microsoft\.Graph\.PowerShell\.Runtime\.Json\.JsonNode\)\s*(.*)\s*:\s*null\s*,\s*"(.*?)"\s*,\s*container\.Add\s*\)/gm, 'container.Add("$3", $1 != null ? (Microsoft.Graph.PowerShell.Runtime.Json.JsonNode) $2 :"defaultnull")')
+        
+        $ = $.replace(/AddIf\(\s*null\s*!=\s*\(\(\(\(object\)\s*(this\._\w+)\)\)?.ToString\(\)\)\s*\?\s*\(\s*Microsoft\.Graph\.PowerShell\.Runtime\.Json\.JsonNode\)\s*new\s*Microsoft\.Graph\.PowerShell\.Runtime\.Json\.JsonString\((this\._\w+).ToString\(\)\)\s*:\s*null\s*,\s*"(.*?)"\s*,\s*container\.Add\s*\)/gm, 'container.Add("$3", $1 != null ? (Microsoft.Graph.PowerShell.Runtime.Json.JsonNode) new Microsoft.Graph.PowerShell.Runtime.Json.JsonString($2.ToString()) :"defaultnull)');
+
         return $;
       }
 # Modify generated .dictionary.cs model classes.