Refactor required fields check on Bulk CSV upload (#59)

Related to https://github.com/etkecc/synapse-admin/pull/32

src/components/ImportFeature.tsx

@@ -121,11 +121,7 @@ const FilePicker = () => {
 
   const verifyCsv = ({ data, meta, errors }: ParseResult<ImportLine>, { setValues, setStats, setError }) => {
     /* First, verify the presence of required fields */
-    const missingFields = expectedFields.filter(eF => {
-      const result = meta.fields?.find(mF => eF === mF);
-      if (result === undefined) { return eF; } // missing field
-      return undefined; // field found
-    });
+    const missingFields = expectedFields.filter(eF => !meta.fields?.find(mF => eF === mF));
 
     if (missingFields.length > 0) {
       setError(translate("import_users.error.required_field", { field: missingFields[0] }));