public Schema build() {
            return new Schema(this);
        }
Looks up a field or field set by the given name or alias in this schema.

@param fieldName the name or alias of the field or field set. If this is empty, the name "default" is looked up
@return information about the field or field set with the given name, or empty if no item with this name exists
container-search/src/main/java/com/yahoo/search/schema/Schema.java