From 3dd72b84ee1acb313ff3a9f8ef6ff0da08a8754a Mon Sep 17 00:00:00 2001
From: Rustam Sayfutdinov <rstm.sf@gmail.com>
Date: Tue, 25 Feb 2020 22:16:07 +0300
Subject: [PATCH] Fix throws exception by \color

---
 src/WpfMath.Tests/ParserExceptionTests.fs | 5 +++++
 src/WpfMath/TexFormulaParser.cs           | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/WpfMath.Tests/ParserExceptionTests.fs b/src/WpfMath.Tests/ParserExceptionTests.fs
index 8a34f699..7540852f 100644
--- a/src/WpfMath.Tests/ParserExceptionTests.fs
+++ b/src/WpfMath.Tests/ParserExceptionTests.fs
@@ -52,6 +52,11 @@ let ``"\binom{}" should throw a TexParseException``(): unit =
     let ex = assertParseThrows<TexParseException> @"\binom{}"
     Assert.Equal("An element is missing", ex.Message)
 
+[<Fact>]
+let ``"\color" should throw a TexParseException``(): unit =
+    let ex = assertParseThrows<TexParseException> @"\color"
+    Assert.Equal("An element is missing", ex.Message)
+
 [<Fact>]
 let ``"\color{red}" should throw a TexParseException``(): unit =
     let ex = assertParseThrows<TexParseException> @"\color{red}"
diff --git a/src/WpfMath/TexFormulaParser.cs b/src/WpfMath/TexFormulaParser.cs
index 0611813a..9679a987 100644
--- a/src/WpfMath/TexFormulaParser.cs
+++ b/src/WpfMath/TexFormulaParser.cs
@@ -349,7 +349,7 @@ private static SourceSpan ReadElementGroupOptional(
             char closeChar)
         {
             SkipWhiteSpace(value, ref position);
-            if (value[position] != openChar)
+            if (position == value.Length || value[position] != openChar)
                 return null;
 
             return ReadElementGroup(value, ref position, openChar, closeChar);