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, 1 insertions, 19 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/mysql/column.rb b/activerecord/lib/active_record/connection_adapters/mysql/column.rb
index 5452e44c84..72b57f4b8f 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/column.rb
@@ -2,17 +2,7 @@ module ActiveRecord
   module ConnectionAdapters
     module MySQL
       class Column < ConnectionAdapters::Column # :nodoc:
-        delegate :strict, :extra, to: :sql_type_metadata, allow_nil: true
-
-        def initialize(*)
-          super
-          extract_default
-        end
-
-        def has_default?
-          return false if blob_or_text_column? # MySQL forbids defaults on blob and text columns
-          super
-        end
+        delegate :extra, to: :sql_type_metadata, allow_nil: true
 
         def blob_or_text_column?
           /\A(?:tiny|medium|long)?blob\b/ === sql_type || type == :text
@@ -29,14 +19,6 @@ module ActiveRecord
         def auto_increment?
           extra == "auto_increment"
         end
-
-        private
-
-          def extract_default
-            if blob_or_text_column?
-              @default = null || strict ? nil : ""
-            end
-          end
       end
     end
   end