refactor: included checkifnull function, added sql schema for the signature database

gaseous-tools/Common.cs

@@ -0,0 +1,24 @@
+using System;
+namespace gaseous_tools
+{
+	public class Common
+	{
+		/// <summary>
+		/// Returns IfNullValue if the ObjectToCheck is null
+		/// </summary>
+		/// <param name="ObjectToCheck">Any nullable object to check for null</param>
+		/// <param name="IfNullValue">Any object to return if ObjectToCheck is null</param>
+		/// <returns></returns>
+		static public object ReturnValueIfNull(object? ObjectToCheck, object IfNullValue)
+		{
+			if (ObjectToCheck == null)
+			{
+				return IfNullValue;
+			} else
+			{
+				return ObjectToCheck;
+			}
+		}
+	}
+}
+