function CONV() returns null when passing a parameter

[PORTE]

The function CONV() returns null value when we use it on a table's column.

without table selection :
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select conv(6906195,10,36);
440UR
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But with a parameter (int(10)) it returns NULL :
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select conv(id,10,36)), id from test ;
NULL 6906195
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When we change the ENGINE to MyIsam it's working.

It works too with conversion from 10 to 2/4/8/16 and reverse conversion from 36 to 10.