Remove text default treated as an empty string in non-strict mode

Strict mode controls how MySQL handles invalid or missing values in
data-change statements such as INSERT or UPDATE. If strict mode is not
in effect, MySQL inserts adjusted values for invalid or missing values
and produces warnings.

```ruby
  def test_mysql_not_null_defaults_non_strict
    using_strict(false) do
      with_mysql_not_null_table do |klass|
        record = klass.new
        assert_nil record.non_null_integer
        assert_nil record.non_null_string
        assert_nil record.non_null_text
        assert_nil record.non_null_blob

        record.save!
        record.reload

        assert_equal 0,  record.non_null_integer
        assert_equal "", record.non_null_string
        assert_equal "", record.non_null_text
        assert_equal "", record.non_null_blob
      end
    end
  end
```

It is inconsistent with other types that only text/blob defaults treated
as an empty string. This commit fixes the inconsistency.

1 files changed, 3 insertions, 4 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb b/activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb
index 1be5cb4740..24dcf852e1 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb
@@ -2,13 +2,12 @@ module ActiveRecord
   module ConnectionAdapters
     module MySQL
       class TypeMetadata < DelegateClass(SqlTypeMetadata) # :nodoc:
-        attr_reader :extra, :strict
+        attr_reader :extra
 
-        def initialize(type_metadata, extra: "", strict: false)
+        def initialize(type_metadata, extra: "")
           super(type_metadata)
           @type_metadata = type_metadata
           @extra = extra
-          @strict = strict
         end
 
         def ==(other)
@@ -24,7 +23,7 @@ module ActiveRecord
         protected
 
           def attributes_for_hash
-            [self.class, @type_metadata, extra, strict]
+            [self.class, @type_metadata, extra]
           end
       end
     end