Introduced InvalidOperationException

Fixes #4425

logstash-core-event/lib/logstash/event.rb

@@ -16,6 +16,9 @@ require "logstash/string_interpolation"
 class LogStash::ShutdownEvent; end
 class LogStash::FlushEvent; end
 
+# Custom exceptions
+class InvalidOperationException < StandardError; end
+
 module LogStash
   FLUSH = LogStash::FlushEvent.new
 
@@ -180,7 +183,7 @@ class LogStash::Event
   # Remove a field or field reference. Returns the value of that field when deleted
   def remove(fieldref)
     if fieldref == TIMESTAMP || fieldref == "[#{TIMESTAMP}]"
-      raise TypeError, "The field '@timestamp' must not be removed"
+      raise InvalidOperationException, "The field '@timestamp' must not be removed"
     end
     @accessors.del(fieldref)
   end

logstash-core-event/spec/logstash/event_spec.rb

@@ -336,7 +336,7 @@ describe LogStash::Event do
 
       context "remove" do
         it "should raise an exception if you attempt to remove @timestamp" do
-          expect{subject.remove("@timestamp")}.to raise_error(TypeError)
+          expect{subject.remove("@timestamp")}.to raise_error(InvalidOperationException)
         end
       end
     end