App.find_dir(): Allow return value None

Allow find_dir() to return None in case it couldn't find a directory, that's a legal outcome. Add a boolean parameter "throw" to support throwing an exception if the existence needs to be asserted.
It would probably be nicer for the type checkers to split this up into a throwing and non-throwing function. Postponed.
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/cmds/projects/CmdGetAuthInfo.py

@@ -57,9 +57,12 @@ class CmdGetAuthInfo(Cmd):  # export
 
         # --- Milk jw-pkg repo
         jw_pkg_dir = self.app.find_dir('jw-pkg', pretty = False)
+        if jw_pkg_dir is None:
+            log(DEBUG, 'Can\'t find jw-pkg directory')
+            return None
         if not os.path.isdir(jw_pkg_dir + '/.git'):
             log(DEBUG, f'jw-pkg directory is not a Git repo: {jw_pkg_dir}')
-            return
+            return None
         git_result = await self.app.exec_context.run(
             ['git', '-C', jw_pkg_dir, 'remote', '-v']
         )

src/python/jw/pkg/cmds/projects/CmdTmplDir.py

@@ -22,5 +22,8 @@ class CmdTmplDir(Cmd):  # export
     async def _run(self, args: Namespace) -> None:
         r = []
         for m in args.module:
-            r.append(self.app.tmpl_dir(m))
+            d = self.app.tmpl_dir(m)
+            if d is None:
+                continue
+            r.append(d)
         print(' '.join(r))