Here is what Oracle documentation says about this error:
ORA-06502: PL/SQL: numeric or value error string
Cause: An arithmetic, numeric, string, conversion, or constraint error occurred. For example, this error occurs if an attempt is made to assign the value NULL to a variable declared NOT NULL, or if an attempt is made to assign an integer larger than 99 to a variable declared NUMBER (2).
Action: Change the data, how it is manipulated, or how it is declared so that values do not violate constraints.
More Information:
These could be the errors:
This error mainly occurs due to one of the following:
1. If you assign NULL value to a NOT NULL field.
2. If you assign number which is larger than the precision of the field.
3. If you assign character values greater than the field width.
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