** (ArgumentError) lists in Phoenix.HTML and templates may only contain integers representing bytes, binaries or other lists, got invalid entry: code example

Example: ** (ArgumentError) lists in Phoenix.HTML and templates may only contain integers representing bytes, binaries or other lists, got invalid entry:

I was using content_tag(:input) and didn't give it space for the value spot.

Throws: ** (ArgumentError) lists in Phoenix.HTML and templates may only contain integers representing bytes, binaries or other lists, got invalid entry:
<%= content_tag :input, value: @item.quantity, type: "value", class: "input-xlarge", id: "orderQuantity" %>

works 
<%= content_tag :input, "", value: @item.quantity, type: "value", class: "input-xlarge", id: "orderQuantity" %>