public Schema getSchema() {
        if (application == null)  throw new IllegalStateException("Application not built");
        if (application.schemas().size() != 1)
            throw new IllegalStateException("This call only works if we have 1 schema. Schemas: " +
                                            application.schemas().values());

        return application.schemas().values().stream().findAny().get();
    }
Convenience method to call {@link #getSchema(String)} when there is only a single {@link Schema} object
built. This method will never return null.

@return the built object
@throws IllegalStateException if there is not exactly one search.
config-model/src/main/java/com/yahoo/schema/ApplicationBuilder.java