Don't treat the lack of documentation as an error

Even if there's no docstring, we can still print the type definition.

Furthermore, print "Undocumented" instead of "no documentation found".
The latter looks too close to the error reported when the identifier
couldn't be resolved.

ident.go

@@ -107,6 +107,9 @@ func IdentDoc(id *ast.Ident, info *loader.PackageInfo, prog *loader.Program) (*D
 	}
 
 	_, nodes, _ := prog.PathEnclosingInterval(obj.Pos(), obj.Pos())
+	if len(nodes) == 0 {
+		return nil, fmt.Errorf("No documentation found for %s", obj.Name())
+	}
 	var doc *Doc
 	for _, node := range nodes {
 		switch node.(type) {
@@ -167,5 +170,5 @@ func IdentDoc(id *ast.Ident, info *loader.PackageInfo, prog *loader.Program) (*D
 			}
 		}
 	}
-	return nil, fmt.Errorf("No documentation found for %s", obj.Name())
+	return doc, nil
 }

main.go

@@ -97,6 +97,9 @@ func main() {
 	}
 	fmt.Println(d.Title)
 	fmt.Println()
+	if d.Doc == "" {
+		d.Doc = "Undocumented."
+	}
 	doc.ToText(os.Stdout, d.Doc, indent, preIndent, lineLength)
 }