An electric or magnetic field doesn't need to be absent when an electron passes through a space without deviation. Any of the following conditions may happen:

• Cross fields. When electric and magnetic fields are aligned perpendicularly, they form cross fields. In such a situation, an electron passes undeflected.
• No electric field but magnetic field. When an electron passes parallel or antiparallel to a magnetic field (where the electric field is absent), it suffers no deviation at all.
• No electric and magnetic fields. When an electron passes through a region with no electric and magnetic fields, it passes without deviation.

Hence, we cannot confirm the absence of electric and magnetic fields when an electron passes through a space without deviation.