Object of type 'NoneType' has no len ()

def get_length_of_missing_array (array_of_arrays):

if len(array_of_arrays)==0:
    return 0
else:
    lenlist = [len(i) for i in array_of_arrays ]
    print(lenlist)
    rangelist=[t for t in range(min(lenlist),max(lenlist)+1)]
    print(rangelist)
    missing=set(rangelist)-set(lenlist)
    return missing.pop()
   

will prompt: object of type "NoneType" has no len ()
the error line is: lenlist = [len (i) for i in array_of_arrays]
but I don"t quite understand why this sentence has this error. Please help me explain it. Thank you

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Mar.07,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3893f-2c11a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3893f-2c11a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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