no ns for keyword

src/data/json.rs

@@ -83,7 +83,7 @@ impl TryFrom<&'_ JsonValue> for Attribute {
             .ok_or_else(|| JsonError::MissingField(value.clone(), "keyword".to_string()))?;
         let keyword = Keyword::try_from(keyword)?;
         if keyword.is_reserved() {
-            return Err(KeywordError::ReservedKeyword(keyword.clone()).into());
+            return Err(KeywordError::ReservedKeyword(keyword).into());
         }
         let cardinality = map
             .get("cardinality")

src/data/keyword.rs

@@ -49,9 +49,21 @@ impl TryFrom<&[u8]> for Keyword {
 
 impl Keyword {
     pub(crate) fn is_reserved(&self) -> bool {
-        self.0.starts_with('_')
+        self.0.is_empty() || self.0.starts_with(['_', ':'])
     }
     pub(crate) fn to_string_no_prefix(&self) -> String {
         format!("{}", self.0)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::data::keyword::Keyword;
+
+    #[test]
+    fn reserved_kw() {
+        assert!(Keyword("_a".into()).is_reserved());
+        assert!(Keyword(":a".into()).is_reserved());
+        assert!(Keyword("".into()).is_reserved());
+    }
+}