Fixed a bug in AttributeMap, which causes a ConcurrentModificationExc…

…eption when lazy properties depend on lazy properties that depend on any other property.

This is achieved by changing a `compute` into a `get` followed by a `put`.

utils/src/main/java/software/amazon/awssdk/utils/AttributeMap.java

@@ -319,6 +319,7 @@ private void internalPut(Key<?> key, Value<?> value) {
             if (oldValue != null) {
                 dependencyGraph.valueUpdated(oldValue, value);
             }
+
         }
 
         /**
@@ -327,17 +328,17 @@ private void internalPut(Key<?> key, Value<?> value) {
          */
         private Value<?> internalComputeIfAbsent(Key<?> key, Supplier<Value<?>> value) {
             checkCopyOnUpdate();
-            return attributes.compute(key, (k, v) -> {
-                if (v == null || resolveValue(v) == null) {
-                    Value<?> newValue = value.get();
-                    Validate.notNull(newValue, "Supplied value must not be null.");
-                    if (v != null) {
-                        dependencyGraph.valueUpdated(v, newValue);
-                    }
-                    return newValue;
+            Value<?> currentValue = attributes.get(key);
+            if (currentValue == null || resolveValue(currentValue) == null) {
+                Value<?> newValue = value.get();
+                Validate.notNull(newValue, "Supplied value must not be null.");
+                if (currentValue != null) {
+                    dependencyGraph.valueUpdated(currentValue, newValue);
                 }
-                return v;
-            });
+                attributes.put(key, newValue);
+                return newValue;
+            }
+            return currentValue;
         }
 
         private void checkCopyOnUpdate() {