meh, null check some other bizstring library functions while I'm thinking about it

BizHawk.Client.Common/lua/EmuLuaLibrary.String.cs

@@ -62,6 +62,11 @@ namespace BizHawk.Client.Common
 		)]
 		public static string Trim(string str)
 		{
+			if (string.IsNullOrEmpty(str))
+			{
+				return null;
+			}
+
 			return str.Trim();
 		}
 
@@ -71,6 +76,11 @@ namespace BizHawk.Client.Common
 		)]
 		public static string Replace(string str, string str2, string replace)
 		{
+			if (string.IsNullOrEmpty(str))
+			{
+				return null;
+			}
+
 			return str.Replace(str2, replace);
 		}
 
@@ -80,6 +90,11 @@ namespace BizHawk.Client.Common
 		)]
 		public static string ToUpper(string str)
 		{
+			if (string.IsNullOrEmpty(str))
+			{
+				return null;
+			}
+
 			return str.ToUpper();
 		}
 
@@ -89,6 +104,11 @@ namespace BizHawk.Client.Common
 		)]
 		public static string ToLower(string str)
 		{
+			if (string.IsNullOrEmpty(str))
+			{
+				return null;
+			}
+
 			return str.ToLower();
 		}
 
@@ -98,6 +118,11 @@ namespace BizHawk.Client.Common
 		)]
 		public static string SubString(string str, int position, int length)
 		{
+			if (string.IsNullOrEmpty(str))
+			{
+				return null;
+			}
+
 			return str.Substring(position, length);
 		}
 
@@ -107,6 +132,11 @@ namespace BizHawk.Client.Common
 		)]
 		public static string Remove(string str, int position, int count)
 		{
+			if (string.IsNullOrEmpty(str))
+			{
+				return null;
+			}
+
 			return str.Remove(position, count);
 		}
 
@@ -116,6 +146,11 @@ namespace BizHawk.Client.Common
 		)]
 		public static bool Contains(string str, string str2)
 		{
+			if (string.IsNullOrEmpty(str))
+			{
+				return false;
+			}
+
 			return str.Contains(str2);
 		}
 
@@ -125,6 +160,11 @@ namespace BizHawk.Client.Common
 		)]
 		public static bool StartsWith(string str, string str2)
 		{
+			if (string.IsNullOrEmpty(str))
+			{
+				return false;
+			}
+
 			return str.StartsWith(str2);
 		}
 
@@ -134,6 +174,11 @@ namespace BizHawk.Client.Common
 		)]
 		public static bool EndsWith(string str, string str2)
 		{
+			if (string.IsNullOrEmpty(str))
+			{
+				return false;
+			}
+
 			return str.EndsWith(str2);
 		}