Normalize relation case when combining license expressions

Signed-off-by: Ali Zulfiqar <codewithfourtix@gmail.com>

Author: codewithfourtix

src/license_expression/__init__.py

@@ -1825,5 +1825,5 @@ def combine_expressions(
     if len(expressions) == 1:
         return expressions[0]
 
-    relation = {"AND": licensing.AND, "OR": licensing.OR}[relation]
+    relation = {"AND": licensing.AND, "OR": licensing.OR}[relation.upper()]
     return relation(*expressions)

tests/test_license_expression.py

@@ -2640,3 +2640,9 @@ def test_combine_expressions_with_duplicated_elements(self):
 
     def test_combine_expressions_with_or_relationship(self):
         assert str(combine_expressions(["mit", "apache-2.0"], "OR")) == "mit OR apache-2.0"
+
+
+def test_combine_expressions_accepts_case_insensitive_relations():
+    for relation in ("and", "And", "AND", "or", "Or", "OR"):
+        result = combine_expressions(["mit", "apache-2.0"], relation=relation)
+        assert str(result) == f"mit {relation.upper()} apache-2.0"