If you bump into ActiveStorage::InvariableError

Turns out the content_type of one ActiveStorage::Blob record has invalid value (text/html). Fixing the record as well as the application code that detected the content_type incorrectly solved the problem for me. YMMV.

The error was raised when I invoke the #variant method on an ActiveStorage Attachment object.

user.avatar.variant(resize_to_fit: [36, 36])
# ActiveStorage::InvariableError!
user.avatar.blob.content_type
# "text/html"

Backtrace:

app/models/active_storage/blob/representable.rb:38:in `variant'
app/models/active_storage/attachment.rb:66:in `variant'
app/helpers/users_helper.rb:16:in `avatar'

ActiveStorage expects these content types:

ActiveStorage.variable_content_types
=> 
["image/png",                                         
 "image/gif",
 "image/jpg",
 "image/jpeg",
 "image/pjpeg",
 "image/tiff",
 "image/bmp",
 "image/vnd.adobe.photoshop",
 "image/vnd.microsoft.icon",
 "image/webp",
 "image/avif",
 "image/heic",
 "image/heif"]