Fixed migration for mat assignment rule

app/models/mat_assignment_rule.rb

@@ -1,4 +1,12 @@
 class MatAssignmentRule < ApplicationRecord
-    belongs_to :mat
-    belongs_to :tournament
-  end
+  belongs_to :mat
+  belongs_to :tournament
+
+  # Ensure default values for JSON fields
+  # because mysql doesn't allow this
+  after_initialize do
+    self.weight_classes ||= []
+    self.bracket_positions ||= []
+    self.rounds ||= []
+  end
+end