@Override
    public boolean exists(final MapDefinition mapDefinition) {
        return mapDefinitionUIDStore.exists(mapDefinition);
    }
Returns true if this {@link MapDefinition} exists in the store. It makes no guarantees about the state
of the data.

@param mapDefinition
stroom-pipeline/src/main/java/stroom/pipeline/refdata/store/offheapstore/RefDataOffHeapStore.java