Merge PR #27202 fix/capa/empty-option-text

* Commits:
  fix: Allow capa_problem optioninput option with empty text
  refactor: Refactor capa_problem optioninput option text handling

common/lib/capa/capa/capa_problem.py

@@ -285,7 +285,9 @@ class LoncapaProblem(object):
             correct_option = None
             child_options = []
             for option_element in optioninput.findall('./option'):
-                option_name = option_element.text.strip()
+                text = option_element.text
+                text = text or ''
+                option_name = text.strip()
                 if option_element.get('correct').upper() == 'TRUE':
                     correct_option = option_name
                 child_options.append("'" + option_name + "'")

common/lib/capa/capa/tests/test_capa_problem.py

@@ -397,6 +397,26 @@ class CAPAProblemTest(unittest.TestCase):
         problem = new_loncapa_problem(xml.format(correctness=False))
         assert problem is not None
 
+    def test_optionresponse_option_with_empty_text(self):
+        """
+        Verify successful instantiation of an optionresponse problem
+        with an option with empty text
+        """
+        xml = """
+        <problem>
+            <optionresponse>
+                <label>Select True or False</label>
+                <optioninput>
+                    <option correct="False">True <optionhint>Not this one</optionhint></option>
+                    <option correct="True">False</option>
+                    <option correct="False"><optionhint>Not this empty one either</optionhint></option>
+                </optioninput>
+            </optionresponse>
+        </problem>
+        """
+        problem = new_loncapa_problem(xml)
+        assert problem is not None
+
 
 @ddt.ddt
 class CAPAMultiInputProblemTest(unittest.TestCase):