From 207377696666ae59a74113492fb35df8d71ea572 Mon Sep 17 00:00:00 2001
From: Dan Moseley <danmose@microsoft.com>
Date: Fri, 26 Jul 2019 14:00:30 -0700
Subject: [PATCH] Update to MatchEvaluator NRE change (dotnet/corefx#39813)

* Update to MatchEvaluator NRE change

* lowercase


Commit migrated from https://github.com/dotnet/corefx/commit/c4e71057d8f2d9717316939584ef046147cefe2f
---
 .../src/System/Text/RegularExpressions/Regex.Replace.cs               | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/Regex.Replace.cs b/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/Regex.Replace.cs
index cb78992..0d94527 100644
--- a/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/Regex.Replace.cs
+++ b/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/Regex.Replace.cs
@@ -186,7 +186,9 @@ namespace System.Text.RegularExpressions
                             vsb.Append(input.AsSpan(prevat, match.Index - prevat));
 
                         prevat = match.Index + match.Length;
-                        vsb.Append(evaluator(match) ?? "");
+                        string result = evaluator(match);
+                        if (!string.IsNullOrEmpty(result))
+	                        vsb.Append(result);
 
                         if (--count == 0)
                             break;
-- 
2.7.4