isSolid property
Whether the symbol should be rendered as a solid shape, or a hollow shape.
If this is true, then fillColor and strokeColor will be used to fill in the shape, and draw a border, respectively. The stroke (border) will only be visible if a non-zero strokeWidthPx is configured.
If this is false, then the shape will be filled in with a white color (overriding fillColor). strokeWidthPx will default to 2 if none was configured.
Implementation
final bool isSolid;