| This checker looks for comparisons of protocol buffer fields with null via the | |
| com.google.common.base.Preconditions.checkNotNull method. If a proto field is | |
| not specified, its field accessor will return a non-null default value. Thus, | |
| the result of calling one of these accessors can never be null, and comparisons | |
| like these often indicate a nearby error. | |
| If you meant to check whether an optional field has been set, you should use the | |
| hasField() method instead. |