fix(load): handle empty column headers on feed load

fixes #124

Author: landonreed

Diff for: src/main/java/com/conveyal/gtfs/error/NewGTFSErrorType.java

@@ -12,6 +12,7 @@ public enum NewGTFSErrorType {
     LANGUAGE_FORMAT(Priority.LOW, "Language should be specified with a valid BCP47 tag."),
     INTEGER_FORMAT(Priority.MEDIUM, "Incorrect integer format."),
     FLOATING_FORMAT(Priority.MEDIUM, "Incorrect floating point number format."),
+    COLUMN_NAME_INVALID(Priority.HIGH, "Column header is not permitted."),
     COLUMN_NAME_UNSAFE(Priority.HIGH, "Column header contains characters not safe in SQL, it was renamed."),
     NUMBER_PARSING(Priority.MEDIUM, "Unable to parse number from value."),
     NUMBER_NEGATIVE(Priority.MEDIUM, "Number was expected to be non-negative."),

Diff for: src/main/java/com/conveyal/gtfs/loader/JdbcGtfsLoader.java

@@ -320,11 +320,14 @@ private int loadInternal (Table table) throws Exception {
         int keyFieldIndex = -1;
         for (int h = 0; h < headerCount; h++) {
             String header = sanitize(csvReader.getHeader(h));
-            if (fieldsSeen.contains(header) || "id".equals(header)) {
-                // FIXME: add separate error for tables containing ID field.
+            if (fieldsSeen.contains(header)) {
                 errorStorage.storeError(NewGTFSError.forTable(table, DUPLICATE_HEADER).setBadValue(header));
                 fields[h] = null;
-            } else {
+            } else if ("id".equals(header) || header.isEmpty()) {
+                // Header field cannot be "id" or missing.
+                errorStorage.storeError(NewGTFSError.forTable(table, COLUMN_NAME_INVALID).setBadValue(header));
+                fields[h] = null;
+            }  else {
                 fields[h] = table.getFieldForName(header);
                 fieldsSeen.add(header);
                 if (keyField.equals(header)) {