Reject Function

I don't understand the purpose of removing holdCode from the cdt if it is null and only show the account id in that case.

But if I can understand the requirement correctly then you will be wanting to implement it as follows:

a!localVariables(
  local!map: {
    a!map(
      id: 1,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test", holdCode: "")
    ),
    a!map(
      id: 2,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test1", holdCode: "abcd")
    ),
    a!map(
      id: 3,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test2", holdCode: "")
    )
  },
  a!forEach(
    items: local!map,
    expression: if(
      isnull(
        index(fv!item, "account", "holdCode", null)
      ),
      updatedictionary(
        fv!item,
        { account: { id: fv!item.account.id } }
      ),
      fv!item
    )
  )
)

I don't understand the purpose of removing holdCode from the cdt if it is null and only show the account id in that case.

But if I can understand the requirement correctly then you will be wanting to implement it as follows:

a!localVariables(
  local!map: {
    a!map(
      id: 1,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test", holdCode: "")
    ),
    a!map(
      id: 2,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test1", holdCode: "abcd")
    ),
    a!map(
      id: 3,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test2", holdCode: "")
    )
  },
  a!forEach(
    items: local!map,
    expression: if(
      isnull(
        index(fv!item, "account", "holdCode", null)
      ),
      updatedictionary(
        fv!item,
        { account: { id: fv!item.account.id } }
      ),
      fv!item
    )
  )
)

Thanks for the solution

But the purpose was not to remove the hold code ... The purpose was to just retain the map who actually has a hold code and ignore the ones that doesn't

GautamShenoy said:

but then my requirement is that the ID should remain in the output

Then what about this that you have mentioned above in the description?

Sorry I framed the question wrong maybe ... I want the entire map to persist whose account have a hold code ... The other maps should be ignored .... Thanks for correcting and sorry for the error

Then, just make a slight change in the code.

a!localVariables(
  local!map: {
    a!map(
      id: 1,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test", holdCode: "")
    ),
    a!map(
      id: 2,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test1", holdCode: "abcd")
    ),
    a!map(
      id: 3,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test2", holdCode: "")
    )
  },
  reject(
    isnull(_),
    a!forEach(
      items: local!map,
      expression: if(
        isnull(
          index(fv!item, "account", "holdCode", null)
        ),
        null,
        fv!item
      )
    )
  )
)

edit: Even simpler 

a!localVariables(
  local!map: {
    a!map(
      id: 1,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test", holdCode: "")
    ),
    a!map(
      id: 2,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test1", holdCode: "abcd")
    ),
    a!map(
      id: 3,
      account: 'type!{urn:com:appian:types:PA}PA_accountTemp'(id: 1, name: "test2", holdCode: "")
    )
  },
  remove(
    local!map,
    wherecontains(null, local!map.account.holdCode)
  )
)

Thank you so much