Java bad version check should return a false, not nil

Fixes #3824

lib/logstash/util/java_version.rb

@@ -53,7 +53,7 @@ module LogStash::Util::JavaVersion
     return nil if version_string.nil?
 
     parsed = parse_java_version(version_string)
-    return nil unless parsed
+    return false unless parsed
 
     if parsed[:major] == 1 && parsed[:minor] == 7 && parsed[:patch] == 0 && parsed[:update] < 51
       true