Empty XML report return no lines

[madest92]

If there are no tests in the project(coberture file is empty), then diff-cover does not see the changes.
I have added new code. And expect coverage difference to be 0.

# git diff origin/master
....
+
+// ToUpper stub. 
+func (i *Implementation) ToUpper(ctx context.Context, req *desc.StringRequest) (*desc.StringResponse, error) {
+    if (req.S=="a") {
+        return nil, nil
+    }
+    return &desc.StringResponse{S: strings.ToUpper(req.S)}, nil
+}

# cat cover.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE coverage SYSTEM "http://cobertura.sourceforge.net/xml/coverage-04.dtd">
<coverage line-rate="NaN" branch-rate="0" version="" timestamp="1668675986513" lines-covered="0" lines-valid="0" branches-covered="0" branches-valid="0" complexity="0">
  <sources></sources>
  <packages></packages>
</coverage>

But I'm getting:

# diff-cover cover.xml --compare-branch origin/master
-------------
Diff Coverage
Diff: origin/master...HEAD, staged and unstaged changes
-------------
No lines with coverage information in this diff.
-------------