```ruby
require 'json'
require "json/merge_patch/version"

module JSON
  MergeError = Class.new(StandardError)

  def self.merge(document, merge_patch)
    document = JSON.parse(document)
    merge_patch = JSON.parse(merge_patch)

    if merge_patch.is_a? Array
      return JSON.dump(merge_patch)
    end

    if document.is_a? Array
      return JSON.dump(merge_patch)
    end

    if merge_patch.is_a? Hash
      document.merge!(merge_patch)
      document.delete_if {|k, v| v.nil? }
      return JSON.dump(document)
    end
  rescue 
    raise MergeError
  end
end
```

Implement a basic recursive_delete_if that passes the failing test.
user
```ruby
require 'json'
require "json/merge_patch/version"

module JSON
  MergeError = Class.new(StandardError)

  def self.merge(document, merge_patch)
    document = JSON.parse(document)
    merge_patch = JSON.parse(merge_patch)

    if merge_patch.is_a? Array
      return JSON.dump(merge_patch)
    end

    if document.is_a? Array
      return JSON.dump(merge_patch)
    end

    if merge_patch.is_a? Hash
      document.merge!(merge_patch)
      document.delete_if(&method(:recursive_delete_if))
      return JSON.dump(document)
    end
  rescue
    raise MergeError
  end

  def self.recursive_delete_if(key, value)
    if value.kind_of?(Hash)
      value.delete_if(&method(:recursive_delete_if))
      nil
    else
      value.nil?
    end
  end
end
```
assistant