enable missing optional csv files

Author: Aurashk

src/input.rs

@@ -56,6 +56,10 @@ pub fn read_csv<'a, T: DeserializeOwned + 'a>(
 pub fn read_csv_optional<'a, T: DeserializeOwned + 'a>(
     file_path: &'a Path,
 ) -> Result<impl Iterator<Item = T> + 'a> {
+    if !file_path.exists() {
+        return Ok(Vec::new().into_iter());
+    }
+
     let vec = read_csv_internal(file_path)?;
     Ok(vec.into_iter())
 }
@@ -347,6 +351,20 @@ mod tests {
                 .next()
                 .is_none()
         );
+
+        // Missing file
+        let dir = tempdir().unwrap();
+        let file_path = dir.path().join("a_missing_file.csv");
+        assert!(!file_path.exists());
+        assert!(read_csv::<Record>(&file_path).is_err());
+        // optional csv's should return empty iterator
+        assert!(
+            read_csv_optional::<Record>(&file_path)
+                .unwrap()
+                .peekable()
+                .peek()
+                .is_none()
+        );
     }
 
     #[test]