Empty glyphs (like the space glyph) don’t have outlines but they do have an advance width. In a Glyph panel you can change an empty glyph into a simple glyph by adding contours. You can also change an empty glyph into a composite glyph by adding Composite Glyph Members.

Clear Glyph

Select Clear Glyph from the Glyph menu, or the Clear toolbar button from the Tools toolbar to delete the outlines from a glyph. This will also remove any color data if performed from the Font panel. If this action is performed from within a glyph panel, then only the outline for the active layer will be deleted.