public void setGlobalPhaseExpression(String expression) {
        verifyThat(globalPhaseExpression == null, "already has global-phase expression");
        this.globalPhaseExpression = expression;
    }
This class holds the extracted information after parsing a
rank-profile block in a schema (.sd) file, using simple data
structures as far as possible.  Do not put advanced logic here!

@author arnej27959
config-model/src/main/java/com/yahoo/schema/parser/ParsedRankProfile.java