public default Set<VertexComputeKey> getVertexComputeKeys() {
        return Collections.emptySet();
    }
The {@link Element} properties that will be mutated during the computation. All properties in the graph are
readable, but only the keys specified here are writable. The default is an empty set.

@return the set of element keys that will be mutated during the vertex program's execution
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/VertexProgram.java