getting error with [DATATYPE_MISMATCH.CAST_WITHOUT_SUGGESTION]

[DATATYPE_MISMATCH.CAST_WITHOUT_SUGGESTION] Cannot resolve “ItemDescriptionSpecification” due to data type mismatch: cannot cast “STRING” to “VOID”. SQLSTATE: 42K09; line 14 pos 2

and my code is
,CAST(‘ND’ AS string) AS ItemDescriptionSpecification

i hvae tried replacing with NULL or some value but still its giving error.
How should i resolve it.