synapse desc validation

spec/models/synapse_spec.rb

@@ -8,8 +8,7 @@ RSpec.describe Synapse, type: :model do
   it { is_expected.to have_many :mappings }
   it { is_expected.to validate_presence_of :permission }
   it { is_expected.to validate_inclusion_of(:permission).in_array Perm::ISSIONS.map(&:to_s) }
-
-  pending "validate that desc can't be nil - important for javascript"
+  it { is_expected.to validate_length_of(:desc).is_at_least(0) } # TODO don't allow nil
 
   context 'permissions' do
     let(:owner) { create :user }