diff --git a/lib/dynomite/item.rb b/lib/dynomite/item.rb
index ab9b778..348ef4a 100644
--- a/lib/dynomite/item.rb
+++ b/lib/dynomite/item.rb
@@ -94,8 +94,13 @@ def update_attribute(field, value)
     end
 
     def delete_attribute(field)
-      @attrs.delete(field.to_sym)
-      update(@attrs, {validate: false})
+      update_params = {
+        expression_attribute_names: { "#field_0" => field.to_s },
+        update_expression: "REMOVE #field_0",
+        key: self.primary_key,
+        table_name: self.class.table_name
+      }
+      self.class.client.update_item(update_params)
       valid? # ActiveRecord does not have a delete_attribute. Follow update_attribute behavior.
     end
     alias :remove_attribute :delete_attribute
diff --git a/lib/dynomite/item/indexes/finder.rb b/lib/dynomite/item/indexes/finder.rb
index 61cf684..1930e02 100644
--- a/lib/dynomite/item/indexes/finder.rb
+++ b/lib/dynomite/item/indexes/finder.rb
@@ -29,11 +29,7 @@ def find_primary_key_index
     end
 
     def primary_key_found?
-      if @source.composite_key?
-        query_fields.include?(@source.partition_key_field) && query_fields.include?(@source.sort_key_field)
-      else
-        query_fields.include?(@source.partition_key_field)
-      end
+      query_fields.include?(@source.partition_key_field)
     end
 
     # It's possible to have multiple indexes with the same partition and sort key.
diff --git a/lib/dynomite/item/typecaster.rb b/lib/dynomite/item/typecaster.rb
index 5b0cff3..8038e85 100644
--- a/lib/dynomite/item/typecaster.rb
+++ b/lib/dynomite/item/typecaster.rb
@@ -30,7 +30,7 @@ def dump(data, depth=0)
     # The method also helps keep track of where we cast_to_type
     # It's only a few spots this provides an easy to search for it.
     # See: https://v5.docs.rubyonjets.com/docs/database/dynamodb/model/typecasting/
-    FALSEY = [false, 'false', 'FALSE', 0, '0', 'f', 'F', 'off', 'OFF']
+    FALSEY = [nil, false, 'false', 'FALSE', 0, '0', 'f', 'F', 'off', 'OFF']
     def cast_to_type(type, value, on: :read)
       case type
       when :integer
diff --git a/lib/dynomite/item/write/put_item.rb b/lib/dynomite/item/write/put_item.rb
index c20f896..9c99c9e 100644
--- a/lib/dynomite/item/write/put_item.rb
+++ b/lib/dynomite/item/write/put_item.rb
@@ -49,7 +49,7 @@ def permitted_attrs
     end
 
     def handle_conditional_check_failed_exception(exception)
-      if @params[:condition_expression] == check_unique_condition
+      if @params[:condition_expression] == check_unique_params[:condition_expression]
         raise Dynomite::Error::RecordNotUnique.new(not_unique_message)
       else # currently only other case is locking
         raise Dynomite::Error::StaleObject.new(exception.message)
@@ -62,24 +62,26 @@ def not_unique_message
       "A #{@model.class.name} with the primary key #{primary_key_attrs} already exists"
     end
 
+    # https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.ConditionExpressions.html#Expressions.ConditionExpressions.PreventingOverwrites
+    # Examples:
+    #   attribute_not_exists(id)
+    #   attribute_not_exists(category) AND attribute_not_exists(sku)
     def check_unique_params
       if @model.new_record? && !@options[:put]
-        @params.merge!(condition_expression: check_unique_condition)
+        condition_expression = @model.primary_key_fields.map do |field|
+          "attribute_not_exists(##{field})"
+        end.join(" AND ")
+        expression_attribute_names = {}.tap do |attribute_names|
+          @model.primary_key_fields.each do |field|
+            attribute_names["##{field}"] = field
+          end
+        end
+        { condition_expression: condition_expression, expression_attribute_names: expression_attribute_names }
       else
         {}
       end
     end
 
-    # https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.ConditionExpressions.html#Expressions.ConditionExpressions.PreventingOverwrites
-    # Examples:
-    #   attribute_not_exists(id)
-    #   attribute_not_exists(category) AND attribute_not_exists(sku)
-    def check_unique_condition
-      condition_expression = @model.primary_key_fields.map do |field|
-        "attribute_not_exists(#{field})"
-      end.join(" AND ")
-    end
-
     def locking_params
       return {} if @params[:condition_expression] # already set from check_unique_params
       return {} unless @model.class.locking_enabled?