when linetype="solid" is specified for a geom_path that is colored an error occurs

``` r
df2 <- data.frame(x = c(1:10), y = c(1:10), z = 'a')
df2[5:7, 1:2] <- NA
ggplot(df, aes(x, y, color = y)) + geom_path(linetype="solid")         # plot issue an error

Error: geom_path: If you are using dotted or dashed lines, colour, size and linetype must be constant over the line

ggplot(df, aes(x, y, color = y)) + geom_path(linetype=1)         # plot works
```
