How can I know when LASTMOVE in IIB will return true or false?

-- Shared row variable for caching config data. Declared at Global scope.
DECLARE S_ConfigSharedRow SHARED ROW;

CREATE COMPUTE MODULE TheFirstComputeNode
CREATE FUNCTION Main() RETURNS BOOLEAN
BEGIN
    CFGDATA_CACHE_LOCK: BEGIN ATOMIC
        -- If the configuration data is not available in the cache then load it from the CONFIG table
        DECLARE CfgDataRef REFERENCE TO S_ConfigSharedRow.CfgDataCache;
        IF NOT LASTMOVE(CfgDataRef) THEN
            -- Select all the relevant content from the actual database in one go.
            DECLARE DBResults ROW;
            DECLARE RetryCount INTEGER 5;
            SET DBResults.Row[] = PASSTHRU('SELECT * FROM CONFIG');

            -- Typically you would post process the content from the DB into a more amenable 
            -- structure but the following will get the data into the shared variable
            CREATE LASTCHILD OF S_ConfigSharedRow.CfgDataCache FROM DBResults;
        END IF;
    END CFGDATA_CACHE_LOCK;

    -- Config data is now available for use

    RETURN TRUE;
END;
END MODULE;

Hi guys, can I ask which is the scenario that LASTMOVE in this case return true, and which case is false. Thanks all.

My experience with LASTMOVE is that it can return NULL, so better only check for TRUE:

    DECLARE CfgDataRef REFERENCE TO S_ConfigSharedRow.CfgDataCache;
    IF LASTMOVE(CfgDataRef) THEN
        -- Nothing to do
    ELSE
        -- Select all the relevant content ...
    END IF;