public String getApiVersion() {
    return apiVersion;
  }
Constructor for use by jackson to populate this object.

@param apiVersion the api version of this buildfile
@param kind the type of configuration file (always BuildFile)
@param from a {@link BaseImageSpec} for specifying the base image
@param creationTime in milliseconds since epoch or ISO 8601 datetime
@param format of the container, valid values in {@link ImageFormat}
@param environment to write into container
@param labels to write into container metadata
@param volumes directories on container that may hold external volumes
@param exposedPorts a set of ports to expose on the container
@param user the username or id to run the container
@param workingDirectory an absolute path to the default working directory
@param entrypoint the container entry point
@param cmd the container entrypoint command arguments
@param layers a list of {@link LayerSpec} that define the container filesystem
jib-cli/src/main/java/com/google/cloud/tools/jib/cli/buildfile/BuildFileSpec.java