src/main/java/com/conveyal/gtfs/error/NewGTFSError.java
public NewGTFSError addInfo (String key, String value) {
        errorInfo.put(key, value);
        return this;
    }
public NewGTFSError addInfo (String key, String value) {
        errorInfo.put(key, value);
        return this;
    }
Add a single key-value pair of supplemental info to this error.
@return the modified object (builder pattern that allows adding info to newly created error object without assigning to a variable).