If you create a workflow that includes a field value in actions or conditions and it always returns a null value, you could be experiencing an issue with permissions. To resolve this issue, check the Execute As Admin box in the workflow definition.
If you create a workflow that is triggered by the inline edit action, the field value in actions or conditions may return a null value. The reason for this is that the record that the workflow runs on may not be loading completely because of the inline edit action.