ActionView::Template::Error: undefined method `-' for nil:NilClass

[quaasi]

View details in Rollbar: https://rollbar.com/MQA/em/items/98/

NoMethodError: undefined method `-' for nil:NilClass
  File "/var/www/events/releases/20190613185948/app/views/buchung/_form_reductions.html.slim", line 55, in block in _app_views_buchung__form_reductions_html_slim__2855925832585734409_70323816677880
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/helpers/capture_helper.rb", line 39, in block in capture
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/helpers/capture_helper.rb", line 203, in with_output_buffer
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/helpers/capture_helper.rb", line 39, in capture
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/helpers/form_helper.rb", line 450, in form_for
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/simple_form-3.5.1/lib/simple_form/action_view_extensions/form_helper.rb", line 27, in block in simple_form_for
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/simple_form-3.5.1/lib/simple_form/action_view_extensions/form_helper.rb", line 46, in with_simple_form_field_error_proc
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/simple_form-3.5.1/lib/simple_form/action_view_extensions/form_helper.rb", line 26, in simple_form_for
  File "/var/www/events/releases/20190613185948/app/views/buchung/_form_reductions.html.slim", line 1, in _app_views_buchung__form_reductions_html_slim__2855925832585734409_70323816677880
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/template.rb", line 157, in block in render
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/notifications.rb", line 168, in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/template.rb", line 352, in instrument_render_template
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/template.rb", line 155, in render
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/partial_renderer.rb", line 342, in block in render_partial
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/abstract_renderer.rb", line 42, in block in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/notifications.rb", line 166, in block in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/notifications/instrumenter.rb", line 21, in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/notifications.rb", line 166, in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/abstract_renderer.rb", line 41, in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/partial_renderer.rb", line 331, in render_partial
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/partial_renderer.rb", line 310, in render
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/renderer.rb", line 47, in render_partial
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/helpers/rendering_helper.rb", line 35, in render
  File "/var/www/events/releases/20190613185948/app/views/buchung/new.html.slim", line 19, in _app_views_buchung_new_html_slim__2844844575453145995_70323819042740
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/template.rb", line 157, in block in render
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/notifications.rb", line 168, in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/template.rb", line 352, in instrument_render_template
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/template.rb", line 155, in render
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/template_renderer.rb", line 52, in block (2 levels) in render_template
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/abstract_renderer.rb", line 42, in block in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/notifications.rb", line 166, in block in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/notifications/instrumenter.rb", line 21, in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/notifications.rb", line 166, in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/abstract_renderer.rb", line 41, in instrument
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/template_renderer.rb", line 51, in block in render_template
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/template_renderer.rb", line 59, in render_with_layout
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/template_renderer.rb", line 50, in render_template
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/template_renderer.rb", line 14, in render
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/renderer.rb", line 42, in render_template
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/renderer/renderer.rb", line 23, in render
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/rendering.rb", line 103, in _render_template
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/action_controller/metal/streaming.rb", line 217, in _render_template
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionview-5.1.6/lib/action_view/rendering.rb", line 83, in render_to_body
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/action_controller/metal/rendering.rb", line 52, in render_to_body
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/action_controller/metal/renderers.rb", line 141, in render_to_body
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/abstract_controller/rendering.rb", line 24, in render
  File "/var/www/events/shared/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/action_controller/metal/rendering.rb", line 36, in render
  File "/var/www/events/shared/bundle/ruby/2.4.0