A null check and a comment

Author: eggrobin

unicodetools/src/main/java/org/unicode/props/PropertyParsingInfo.java

@@ -690,6 +690,9 @@ static void parseSourceFile(
                                 && indexUnicodeProperties.ucdVersion.compareTo(
                                                 VersionInfo.UNICODE_6_3)
                                         <= 0) {
+                            // Old versions of MathClassEx had a malformed range and a line that
+                            // should have been commented out.  Search for those specifically and
+                            // fix them; we don’t want to generally allow a new range syntax.
                             parser =
                                     parser.withLinePreprocessor(
                                             s ->

unicodetools/src/main/java/org/unicode/props/PropertyUtilities.java

@@ -73,6 +73,9 @@ public RedundancyIgnoringMultivaluedJoiner() {}
 
         @Override
         public String merge(String first, String second) {
+            if (first == null) {
+                return second;
+            }
             final Set<String> oldValues = Set.of(first.split("\\|"));
             if (second == null || oldValues.contains(second)) {
                 return first;