Fix handling of documents containing only whitespace.

src/parser/document.rs

@@ -3,6 +3,7 @@ use std::path::Path;
 use nom::combinator::all_consuming;
 use nom::combinator::opt;
 use nom::multi::many0;
+use nom::InputTake;
 
 use super::headline::heading;
 use super::in_buffer_settings::apply_in_buffer_settings;
@@ -195,9 +196,9 @@ fn _document<'b, 'g, 'r, 's>(
             zeroth_section,
             children,
             contents: if contents.len() > 0 {
-                Some(Into::<&str>::into(contents))
+                Into::<&str>::into(contents)
             } else {
-                None
+                Into::<&str>::into(remaining.take(0))
             },
         },
     ))