public void setQueryString(String queryString) {
        if (queryString == null) queryString="";
        this.queryString = queryString;
        clearQueryTree();
    }
Set the query from a string. This will not be parsed into a query tree until that tree is attempted accessed.
Note that setting this will clear the current query tree. Usually, this should <i>not</i> be modified -
changes to the query should be implemented as modifications on the query tree structure.
<p>
Passing null causes this to be set to an empty string.
container-search/src/main/java/com/yahoo/search/query/Model.java