private com.google.protobuf.MapField<java.lang.String, java.lang.String>
        internalGetMutableLabels() {
      if (labels_ == null) {
        labels_ = com.google.protobuf.MapField.newMapField(LabelsDefaultEntryHolder.defaultEntry);
      }
      if (!labels_.isMutable()) {
        labels_ = labels_.copy();
      }
      bitField0_ |= 0x00000010;
      onChanged();
      return labels_;
    }
<pre>
Optional. The format of the source text, for example, "text/html",
"text/plain". If left blank, the MIME type defaults to "text/html".
</pre>

<code>string mime_type = 3 [(.google.api.field_behavior) = OPTIONAL];</code>

@param value The bytes for mimeType to set.
@return This builder for chaining.
java-translate/proto-google-cloud-translate-v3/src/main/java/com/google/cloud/translate/v3/DetectLanguageRequest.java