driver-legacy/src/main/com/mongodb/QueryBuilder.java
public DBObject get() {
        for (final String key : _query.keySet()) {
            if (_query.get(key) instanceof NullObject) {
                throw new QueryBuilderException("No operand for key:" + key);
            }
        }
        return _query;
    }
public DBObject get() {
        for (final String key : _query.keySet()) {
            if (_query.get(key) instanceof NullObject) {
                throw new QueryBuilderException("No operand for key:" + key);
            }
        }
        return _query;
    }
Creates a {@code DBObject} query to be used for the driver's find operations

@return {@code this}
@throws RuntimeException if a key does not have a matching operand