public Builder setKey(java.lang.String value) {
        if (value == null) {
          throw new NullPointerException();
        }
        key_ = value;
        bitField0_ |= 0x00000001;
        onChanged();
        return this;
      }
<pre>
The Key of the header.
</pre>

<code>string key = 1;</code>

@param value The key to set.
@return This builder for chaining.
java-tasks/proto-google-cloud-tasks-v2beta3/src/main/java/com/google/cloud/tasks/v2beta3/HttpTarget.java