psych/visitors/yaml_tree.rb: skip warning when excpt as last commit says

ext/psych/lib/psych/visitors/yaml_tree.rb

@@ -76,15 +76,20 @@ def accept target
         end
 
         if target.respond_to?(:to_yaml)
-          loc = target.public_method(:to_yaml).source_location.first
-          if loc !~ /(syck\/rubytypes.rb|psych\/core_ext.rb)/
-            unless target.respond_to?(:encode_with)
-              if $VERBOSE
-                warn "implementing to_yaml is deprecated, please implement \"encode_with\""
+          begin
+            loc = target.public_method(:to_yaml).source_location.first
+            if loc !~ /(syck\/rubytypes.rb|psych\/core_ext.rb)/
+              unless target.respond_to?(:encode_with)
+                if $VERBOSE
+                  warn "implementing to_yaml is deprecated, please implement \"encode_with\""
+                end
+
+                target.to_yaml(:nodump => true)
               end
-
-              target.to_yaml(:nodump => true)
             end
+          rescue
+            # public_method or source_location might be overridden,
+            # and it's OK to skip it since it's only to emit a warning.
           end
         end
 
@@ -297,12 +302,17 @@ def format_time time
 
       # FIXME: remove this method once "to_yaml_properties" is removed
       def find_ivars target
-        loc = target.public_method(:to_yaml_properties).source_location.first
-        unless loc.start_with?(Psych::DEPRECATED) || loc.end_with?('rubytypes.rb')
-          if $VERBOSE
-            warn "#{loc}: to_yaml_properties is deprecated, please implement \"encode_with(coder)\""
+        begin
+          loc = target.public_method(:to_yaml_properties).source_location.first
+          unless loc.start_with?(Psych::DEPRECATED) || loc.end_with?('rubytypes.rb')
+            if $VERBOSE
+              warn "#{loc}: to_yaml_properties is deprecated, please implement \"encode_with(coder)\""
+            end
+            return target.to_yaml_properties
           end
-          return target.to_yaml_properties
+        rescue
+          # public_method or source_location might be overridden,
+          # and it's OK to skip it since it's only to emit a warning.
         end
 
         target.instance_variables