owner: use missing

Author: scivision

+stdlib/+dotnet/get_owner.m

@@ -5,7 +5,7 @@
 % This is not yet possible with .NET on Unix, even with .NET 10.
 % It would require Pinvoke or external Mono.Unix
 
-o = '';
+o = missing;
 
 try
   ntAccountType = System.Type.GetType('System.Security.Principal.NTAccount');

+stdlib/+java/get_owner.m

@@ -6,7 +6,7 @@
 % https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/nio/file/Files.html#getOwner(java.nio.file.Path,java.nio.file.LinkOption...)
 % https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/nio/file/LinkOption.html
 
-n = '';
+n = missing;
 if stdlib.strempty(file)
   return
 end

+stdlib/+python/get_owner.m

@@ -1,6 +1,6 @@
 function n = get_owner(file)
 
-n = '';
+n = missing;
 
 if stdlib.strempty(file)
   return

+stdlib/+shell/get_owner.m

@@ -1,6 +1,6 @@
 function [o, cmd] = get_owner(file)
 
-o = '';
+o = missing;
 
 if ispc()
   cmd = sprintf('pwsh -c "if($x=Get-Acl -Path ''%s'') {$x.Owner}"', file);

+stdlib/get_owner.m

@@ -13,7 +13,7 @@
   backend (1,:) string = ["java", "dotnet", "python", "shell"]
 end
 
-r = '';
+r = missing;
 
 for b = backend
   switch b
@@ -31,7 +31,7 @@
       error('stdlib:get_owner:ValueError', 'Unknown backend: %s', b)
   end
 
-  if ~isempty(r)
+  if ~ismissing(r)
     return
   end
 end

test/TestDisk.m

@@ -196,16 +196,16 @@ function test_inode(tc, Ps, B_jps)
 function test_owner(tc, Ps, B_jdps)
 [o, b] = stdlib.get_owner(Ps, B_jdps);
 tc.assertMatches(b, B_jdps)
-tc.verifyClass(o, 'char')
 
 if ismember(B_jdps, stdlib.Backend().select('get_owner'))
   if ~stdlib.exists(Ps)
-    tc.verifyEqual(o, '')
+    tc.verifyEqual(o, missing)
   else
+  tc.verifyClass(o, 'char')
     tc.verifyGreaterThan(strlength(o), 0)
   end
 else
-  tc.verifyEmpty(o)
+  tc.verifyEqual(o, missing)
 end
 
 end