3 files changed, 9 insertions, 3 deletions
diff --git a/activerecord/lib/active_record/coders/yaml_column.rb b/activerecord/lib/active_record/coders/yaml_column.rb
index 77af540c3e..66a0c83c41 100644
--- a/activerecord/lib/active_record/coders/yaml_column.rb
+++ b/activerecord/lib/active_record/coders/yaml_column.rb
@@ -15,7 +15,13 @@ module ActiveRecord
       end
 
       def dump(obj)
-        YAML.dump(obj) unless obj.nil?
+        return if obj.nil?
+
+        unless obj.is_a?(object_class)
+          raise SerializationTypeMismatch,
+            "Attribute was supposed to be a #{object_class}, but was a #{obj.class}. -- #{obj.inspect}"
+        end
+        YAML.dump obj
       end
 
       def load(yaml)
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 52e67ecc6e..2c74f4011d 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -200,7 +200,7 @@ module ActiveRecord
         relation = relation.where(table[primary_key].eq(id)) if id
       end
 
-      connection.select_value(relation, "#{name} Exists", relation.bind_values) ? true : false
+      connection.select_value(relation, "#{name} Exists", relation.bind_values)
     end
 
     protected
diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index dcbd165e58..95fd33c1d1 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -40,7 +40,7 @@ module ActiveRecord
       def header(stream)
         define_params = @version ? ":version => #{@version}" : ""
 
-        if stream.respond_to?(:external_encoding)
+        if stream.respond_to?(:external_encoding) && stream.external_encoding
           stream.puts "# encoding: #{stream.external_encoding.name}"
         end