public Schema getSchema(String name) {
        if (application == null)  throw new IllegalStateException("Application not built");
        if (name == null) return getSchema();
        return application.schemas().get(name);
    }
Returns the built {@link Schema} object that has the given name. If the name is unknown, this method will simply
return null.

@param name the name of the schema to return,
            or null to return the only one or throw an exception if there are multiple to choose from
@return the built object, or null if none with this name
@throws IllegalStateException if {@link #build} has not been called.
config-model/src/main/java/com/yahoo/schema/ApplicationBuilder.java