public static IllegalArgumentException memoryAddOnlyDuringVertexProgramExecute(final String key) {
            return new IllegalArgumentException("The memory can only be add() during vertex program execute: " + key);
        }
The Admin interface is used by the {@link GraphComputer} to update the Memory.
The developer should never need to type-cast the provided Memory to Memory.Admin.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/Memory.java