fix: remove unnecessary null check

Author: diegomarquezp

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/protoparser/HttpRuleParser.java

@@ -150,13 +150,7 @@ private static Set<HttpBinding> validateAndConstructHttpBindings(
       List<String> jsonNameParts = new ArrayList();
       for (int i = 0; i < subFields.length; i++) {
         String subFieldName = subFields[i];
-
         Field field = nestedMessage.fieldMap().get(subFieldName);
-        Preconditions.checkState(
-            field != null,
-            "Expected message %s to contain field %s but none found",
-            nestedMessage.name(),
-            subFieldName);
 
         // Each component of the JSON name uses the json_name annotation of the field,
         // or default to the field name