[fix] Handle empty PMID array (#220)

Bug fix to address handling an empty PMID array.

src/index.ts

@@ -29,7 +29,7 @@ async function main() {
 		/** Array of PubMed Central IDs (PMCIDs) for the articles found. */
 		const pmids = await searchArticlesBySpecies(throttle, species);
 
-		if (pmids.length > 0) {
+		if (pmids?.length > 0) {
 			await fetchArticleDetails(throttle, pmids, species);
 		} else {
 			console.log(`No articles found for the species: ${species}.`);

src/processor/fetchArticleDetails.test.ts

@@ -75,4 +75,16 @@ describe("fetchArticleDetails", () => {
 
 		expect(axios.get).toHaveBeenCalledTimes(1); // Should not call axios.get again
 	});
+
+	it("should handle empty PMID array gracefully", async () => {
+		const emptyPmids: string[] = [];
+		const consoleLogSpy = jest.spyOn(console, "log").mockImplementation(() => {});
+
+		await fetchArticleDetails(throttle, emptyPmids, species);
+
+		expect(axios.get).not.toHaveBeenCalled();
+		expect(consoleLogSpy).toHaveBeenCalledWith("No PMC IDs provided for Homo sapiens.");
+
+		consoleLogSpy.mockRestore();
+	});
 });

src/processor/fetchArticleDetails.ts

@@ -43,6 +43,12 @@ export async function fetchArticleDetails(
 		fs.mkdirSync(path.dirname(cachedIDsFilePath), { recursive: true });
 	}
 
+	// Check if PMIDs array is undefined/null or empty
+	if (!pmids || pmids.length === 0) {
+		console.log(`No PMC IDs provided for ${species.replace("_", " ")}.`);
+		return;
+	}
+
 	// Get article details based on PMC IDs
 	for (let i = 0; i < pmids.length; i += batchSize) {
 		// Extract a batch of 50 PMC IDs