fix: fix RetryAfter function when there's no Retry-After header (box/box-codegen#903)

Author: box-sdk-build

.codegen.json

@@ -1 +1 @@
-{ "engineHash": "88d7a7e", "specHash": "31c41d5", "version": "5.2.0" }
+{ "engineHash": "f97463c", "specHash": "31c41d5", "version": "5.2.0" }

src/main/java/com/box/sdkgen/networking/retries/BoxRetryStrategy.java

@@ -67,7 +67,10 @@ public boolean shouldRetry(
   @Override
   public double retryAfter(
       FetchOptions fetchOptions, FetchResponse fetchResponse, int attemptNumber) {
-    String retryAfterHeader = fetchResponse.getHeaders().get("Retry-After");
+    String retryAfterHeader =
+        (fetchResponse.getHeaders().containsKey("Retry-After")
+            ? fetchResponse.getHeaders().get("Retry-After")
+            : null);
     if (!(retryAfterHeader == null)) {
       return Double.parseDouble(retryAfterHeader);
     }