Getting error while I am try to retrieve data ?

local!validDetails: if(
rule!APP_isValid(
local!username,
ri!group
),
displayvalue(
local!username,
index(
ri!employeeInfo,
"LOGIN",
""
),
ri!employeeInfo,
""
),
""
)

The above code is not working as expected, In UI it is throwing error due to invalid user.

If USER is not present I want to show blank .

Can you show what inputs you have provided and what the output of this expression is? Also you mentioned above that you're having an issue with a user picker, but there isn't a user picker in that expression - is there more of the code that includes the picker?

I am getting below error for picker value

Expression evaluation error [evaluation ID = f4152:fa492] in rule 'abs_section_modificationrequest' (called by rules 'abs_section_detailstabs' > 'abs_form_newmodificationrequest') at function a!forEach [line 1577]: Error in a!forEach() expression during iteration 1: Expression evaluation error at function a!pickerFieldUsers [line 1683]: A user picker component [label="User Name"] has an invalid value for "value". All users must be valid and visible to the viewer.

Ok but what about the code of the picker itself? Like Stefan mentioned below, this means the value of your picker is invalid - so what is the current value for your picker?

due to some security reason I can't paste my code here, just want to know how to handle above error if the value is invalid. if picker has invalid value I want to display blank value for picker .

Please try using save!value using a!save() function at value parameter so that the value can be given properly.