"This expression is not callable."

[khansudarsan]

https://github.com/wa0x6e/cal-heatmap/blob/279e4eea42e962daf710ec721871cd5ffca97907/src/calendar/Populator.ts#L37

This expression is not callable. Not all constituents of type 'string | ((timestamp: number, value: string | number | null | undefined, backgroundColor: string) => string)' are callable. Type 'string' has no call signatures.ts(2349) Cannot invoke an object which is possibly 'null'.ts(2721) 'color' is possibly 'null'.ts(18047)

let color: string | ((timestamp: Timestamp, value: number | string | null | undefined, backgroundColor: string) => string) | null

color has two types which is not callable but in the mentioned line above, it's been called without taking care of string and null type.