All File::Copy functions return 1 on success, 0 on failure. autodie appears to expects functions to return undef on failure. Example

C:\strawberry>perl -E "sub moon{rand;0}; use autodie q,moon,; say moon
+;"
0

C:\strawberry>perl -E "sub moon{rand;return}; use autodie q,moon,; say
+ moon;"
Can't moon():  at -e line 1

C:\strawberry>perl -E "sub moon{rand;undef}; use autodie q,moon,; say 
+moon;"
Can't moon():  at -e line 1


C:\strawberry>perl -E "sub moon{rand;0}; use Fatal q,moon,; say moon;"
Can't moon(), $! is "" at (eval 1) line 4
        main::__ANON__() called at -e line 1

C:\strawberry>perl -E "sub moon{rand;return}; use Fatal q,moon,; say m
+oon;"
Can't moon(), $! is "" at (eval 1) line 4
        main::__ANON__() called at -e line 1

C:\strawberry>perl -E "sub moon{rand;undef}; use Fatal q,moon,; say mo
+on;"
Can't moon(), $! is "" at (eval 1) line 4
        main::__ANON__() called at -e line 1

C:\strawberry>
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You should report this, at the very least it is a documentation bug.