old_contents: from django.db import models
  from experiment_session.models import ExperimentSession
  from django.core.validators import MinValueValidator
  
  
  class Experiment(models.Model):
      LIGHTOFF_FIXED = 'fixed'
      LIGHTOFF_WAITING = 'waiting'
      _LIGHTOFF_CHOICES = (
          (LIGHTOFF_FIXED, 'Fixed'),
          (LIGHTOFF_WAITING, 'Waiting')
      )
  
      AUDIO_NONE = 'none'
      AUDIO_BEEP = 'beep'
      _AUDIO_CHOICES = (
          (AUDIO_NONE, 'None'),
          (AUDIO_BEEP, 'Audible beep on error')
      )
  
      name = models.CharField(unique=True, max_length=255)
  
      lightoffmode = models.CharField(
          choices=_LIGHTOFF_CHOICES,
          max_length=30
      )
  
      lightofftimeout = models.IntegerField(validators=(MinValueValidator(0),))
  
      audiomode = models.CharField(
          choices=_AUDIO_CHOICES,
          max_length=30
      )
  
      repeatscount = models.IntegerField(
          validators=(
              MinValueValidator(1),
          )
      )
  
      createdon = models.DateTimeField(auto_now_add=True, editable=False)
  
      traininglength = models.IntegerField(validators=(MinValueValidator(0),))
  
      instructions = models.CharField(max_length=10000, default='')
  
      def __str__(self):
          return self.name
  
new_contents: from django.db import models
  from experiment_session.models import ExperimentSession
  from django.core.validators import MinValueValidator
  
  
  class Experiment(models.Model):
      LIGHTOFF_FIXED = 'fixed'
      LIGHTOFF_WAITING = 'waiting'
      _LIGHTOFF_CHOICES = (
          (LIGHTOFF_FIXED, 'Fixed'),
          (LIGHTOFF_WAITING, 'Waiting')
      )
  
      AUDIO_NONE = 'none'
      AUDIO_BEEP = 'beep'
      _AUDIO_CHOICES = (
          (AUDIO_NONE, 'None'),
          (AUDIO_BEEP, 'Audible beep on error')
      )
  
      name = models.CharField(unique=True, max_length=255)
  
      lightoffmode = models.CharField(
          choices=_LIGHTOFF_CHOICES,
          max_length=30
      )
  
      lightofftimeout = models.IntegerField(validators=(MinValueValidator(0),))
  
      audiomode = models.CharField(
          choices=_AUDIO_CHOICES,
          max_length=30
      )
  
      repeatscount = models.IntegerField(
          validators=(
              MinValueValidator(1),
          )
      )
  
      createdon = models.DateTimeField(auto_now_add=True, editable=False)
  
      traininglength = models.IntegerField(validators=(MinValueValidator(0),))
  
      instructions = models.CharField(max_length=10000, blank=True)
  
      def __str__(self):
          return self.name
  
subject: Allow empty strings as instructions