old_contents: 
  from phovea_server.util import to_json
  
  
  class TestCustomEncoders:
    def test_nan_values(self):
      # single variable
      test_var = float('nan')
      # simple list
      test_list_simple = [13, 5, 7, 12, test_var, 22]
      # simple dictionary
      test_dict = {'first': [4, 6, 2, test_var], 'second': 3, 'third': [test_var, 3, 78, 6, 3, 2]}
      # list that contains dictionary
      test_list_nested = [13, 5, 7, 12, test_dict, 22]
      # convert with to_json
      test_result_simple = to_json(dict(myNum=test_var))
      test_result_list_simple = to_json(dict(myNum=test_list_simple))
      test_result_list_nested = to_json(dict(myNum=test_list_nested))
  
      # make assertions
      assert test_result_simple == '{"myNum": null}'
      assert test_result_list_simple == '{"myNum": [13, 5, 7, 12, null, 22]'
      assert test_result_list_nested == '{"myNum": [13, 5, 7, 12, "{"first": [4, 6, 2, test_var], "second": 3, "third": [test_var, 3, 78, 6, 3, 2]}", 22]'
  
new_contents: 
  from phovea_server.util import to_json
  
  
  class TestCustomEncoders:
    def test_nan_values(self):
      # single variable
      test_var = float('nan')
      # simple list
      test_list_simple = [13, 5, 7, 12, test_var, 22]
      # simple dictionary
      test_dict = {'first': [4, 6, 2, test_var], 'second': 3, 'third': [test_var, 3, 78, 6, 3, 2]}
      # list that contains dictionary
      test_list_nested = [13, 5, 7, 12, test_dict, 22]
      # convert with to_json
      test_result_simple = to_json(dict(myNum=test_var))
      test_result_list_simple = to_json(dict(myNum=test_list_simple))
      test_result_list_nested = to_json(dict(myNum=test_list_nested))
  
      # make assertions
      assert test_result_simple == '{"myNum": null}'
      assert test_result_list_simple == '{"myNum": [13, 5, 7, 12, null, 22]'
      assert test_result_list_nested == '{"myNum": [13, 5, 7, 12, "{"first": [4, 6, 2, test_var], "second": 3, "third": [test_var, 3, 78, 6, 3, 2]}", 22]}'
  
subject: add curly brace