fix: AwsHttpApiV2ProxyHttpServletRequest.getParameterMap returns arrays containing null for empty query params (#427)

Author: deki

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/internal/servlet/AwsHttpApiV2ProxyHttpServletRequest.java

@@ -514,7 +514,7 @@ private MultiValuedTreeMap<String, String> parseRawQueryString(String qs) {
 
                 String[] kv = value.split(QUERY_STRING_KEY_VALUE_SEPARATOR);
                 String key = URLDecoder.decode(kv[0], LambdaContainerHandler.getContainerConfig().getUriEncoding());
-                String val = kv.length == 2 ? kv[1] : null;
+                String val = kv.length == 2 ? kv[1] : "";
                 qsMap.add(key, val);
             } catch (UnsupportedEncodingException e) {
                 log.error("Unsupported encoding in query string key: " + SecurityUtils.crlf(value), e);

aws-serverless-java-container-core/src/test/java/com/amazonaws/serverless/proxy/internal/servlet/AwsProxyHttpServletRequestTest.java

@@ -74,6 +74,8 @@ public class AwsProxyHttpServletRequestTest {
 
     private static final AwsProxyRequestBuilder REQUEST_QUERY = new AwsProxyRequestBuilder("/hello", "POST")
             .queryString(FORM_PARAM_NAME, QUERY_STRING_NAME_VALUE);
+    private static final AwsProxyRequestBuilder REQUEST_QUERY_EMPTY_VALUE = new AwsProxyRequestBuilder("/hello", "POST")
+            .queryString(FORM_PARAM_NAME, "");
 
 
     public AwsProxyHttpServletRequestTest(String type) {
@@ -239,6 +241,14 @@ public void queryParameters_getParameterMap_nonNull() {
         assertEquals(QUERY_STRING_NAME_VALUE, request.getParameterMap().get(FORM_PARAM_NAME)[0]);
     }
 
+    @Test
+    public void queryParameters_getParameterMap_nonNull_EmptyParamValue() {
+        HttpServletRequest request = getRequest(REQUEST_QUERY_EMPTY_VALUE, null, null);
+        assertNotNull(request);
+        assertEquals(1, request.getParameterMap().size());
+        assertEquals("", request.getParameterMap().get(FORM_PARAM_NAME)[0]);
+    }
+
     @Test
     public void queryParameters_getParameterNames_null() {
         HttpServletRequest request = getRequest(REQUEST_NULL_QUERY_STRING, null, null);