src/main/java/com/conveyal/gtfs/util/Util.java
public static void ensureValidNamespace(String namespace) throws InvalidNamespaceException {
        Pattern pattern = Pattern.compile("[^a-zA-Z0-9_\\.]");
        Matcher matcher = pattern.matcher(namespace);
        if (matcher.find()) {
            throw new InvalidNamespaceException();
        }
    }
public static void ensureValidNamespace(String namespace) throws InvalidNamespaceException {
        Pattern pattern = Pattern.compile("[^a-zA-Z0-9_\\.]");
        Matcher matcher = pattern.matcher(namespace);
        if (matcher.find()) {
            throw new InvalidNamespaceException();
        }
    }
Ensures namespace is valid by ensuring it only has alphanumeric characters or the underscore
for all characters in the string
@param namespace