Personally, I've found this to be a very useful tool with people who are conflict-avoidant. I tell them "if you're afraid of offending me, please don't hesitate, I promise I won't get mad".
Sometimes I go as far as to suggest something they might be thinking that might be offensive in order to get the ball rolling and show them there won't be negative consequences.
For example: "Hey I wonder if you're concerned I'll be offended if you propose throwing out my work and replacing it. Don't worry, it's fine. I just want what's best for the project, so if you're holding back because you're concerned I'll be upset, you can relax."