public FieldPath buildFieldPath(String fieldPathString) {
        if (fieldPathString.length() > 0) {
            throw new IllegalArgumentException("Datatype " + this +
                                               " does not support further recursive structure: " + fieldPathString);
        }
        return new FieldPath();
    }
Creates a field path from the given field path string.

@param fieldPathString a string containing the field path
@return Returns a valid field path, parsed from the string
document/src/main/java/com/yahoo/document/DataType.java