Fixed handling of null 'replacement' parameter in RegexReplacement#createRegexReplacement (#3215)

* per other builder methods in Log4j a invalid input parameter should result in a fas-fail returning null

Author: JWT007

log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/RegexReplacement.java

@@ -65,7 +65,7 @@ public String toString() {
      * Create a RegexReplacement.
      * @param regex The regular expression to locate.
      * @param replacement The replacement value.
-     * @return A RegexReplacement.
+     * @return the new RegexReplacement instance or {@code null} if an input parameter was invalid
      */
     @PluginFactory
     public static RegexReplacement createRegexReplacement(
@@ -76,6 +76,7 @@ public static RegexReplacement createRegexReplacement(
         }
         if (replacement == null) {
             LOGGER.error("A replacement string is required to perform replacement");
+            return null;
         }
         // FIXME: should we use Matcher.quoteReplacement() here?
         return new RegexReplacement(regex, replacement);

src/changelog/2.25.0/3215_fix-RegexReplacement.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="3215" link="https://github.com/apache/logging-log4j2/issues/3215"/>
+  <description format="asciidoc">
+    Properly handle null 'replacement' parameter in RegexReplacement#createRegexReplacement.
+  </description>
+</entry>