Fix comparing key and mark prefix/suffix as optional.

src/compare/compare_field.rs

@@ -14,7 +14,6 @@ use crate::types::AstNode;
 #[derive(Debug)]
 pub(crate) enum EmacsField<'s> {
     Required(&'s str),
-    #[allow(dead_code)]
     Optional(&'s str),
 }
 

src/compare/diff.rs

@@ -3492,13 +3492,21 @@ fn compare_citation<'b, 's>(
             compare_property_quoted_string
         ),
         (
-            EmacsField::Required(":prefix"),
-            |r| Some(r.prefix.iter()),
+            EmacsField::Optional(":prefix"),
+            |r| if r.prefix.is_empty() {
+                None
+            } else {
+                Some(r.prefix.iter())
+            },
             compare_property_list_of_ast_nodes
         ),
         (
-            EmacsField::Required(":suffix"),
-            |r| Some(r.suffix.iter()),
+            EmacsField::Optional(":suffix"),
+            |r| if r.suffix.is_empty() {
+                None
+            } else {
+                Some(r.suffix.iter())
+            },
             compare_property_list_of_ast_nodes
         )
     ) {
@@ -3544,13 +3552,21 @@ fn compare_citation_reference<'b, 's>(
             compare_property_quoted_string
         ),
         (
-            EmacsField::Required(":prefix"),
-            |r| Some(r.prefix.iter()),
+            EmacsField::Optional(":prefix"),
+            |r| if r.prefix.is_empty() {
+                None
+            } else {
+                Some(r.prefix.iter())
+            },
             compare_property_list_of_ast_nodes
         ),
         (
-            EmacsField::Required(":suffix"),
-            |r| Some(r.suffix.iter()),
+            EmacsField::Optional(":suffix"),
+            |r| if r.suffix.is_empty() {
+                None
+            } else {
+                Some(r.suffix.iter())
+            },
             compare_property_list_of_ast_nodes
         )
     ) {