Extract github actions utils

src/github-utils.ts

@@ -0,0 +1,9 @@
+import * as core from '@actions/core'
+
+export function inputOrNull(name: string): string | null {
+    const inputString = core.getInput(name, {required: false})
+    if (inputString.length === 0) {
+        return null
+    }
+    return inputString
+}