Settings loader mandatory fixes

- mandatory empty check if empty list ([''])
- skip regex check if replace value is None -> allowed empty as empty if not mandatory

test-run/config_handling/config/settings.ini

@@ -1,6 +1,7 @@
 [TestA]
 foo=bar
 foobar=1
+bar=st
 some_match=foo
 some_match_list=foo,bar
 test_list=a,b,c,d f, g h
@@ -21,5 +22,6 @@ match_source_list=foo,bar
 element_a=Static energy
 element_b=123.5
 element_c=True
-email=foo@bar.com,other+bar-fee@domain-com.cp
-email_bad=@bar.com
+email=foo@bar.com,other+bar-fee@domain-com.cp,
+email_not_mandatory=
+email_bad=gii@bar.com

test-run/config_handling/settings_loader.py

@@ -44,6 +44,7 @@ def main():
             {
                 "foo": ["mandatory:yes"],
                 "foobar": ["check:int"],
+                "bar": ["mandatory:yes"],
                 "some_match": ["matching:foo|bar"],
                 "some_match_list": ["split:,", "matching:foo|bar"],
                 "test_list": [
@@ -82,6 +83,11 @@ def main():
                     "mandatory:yes",
                     "check:string.email.basic"
                 ],
+                "email_not_mandatory": [
+                    "split:,",
+                    # "mandatory:yes",
+                    "check:string.email.basic"
+                ],
                 "email_bad": [
                     "split:,",
                     "mandatory:yes",