code: public String get(String environmentVariableName, String defaultValue) {
      return environmentVariables().get(environmentVariableName, defaultValue);
    }
docs: Returns the value set for the environment variable identified by the given name.  If the environment variable
  is not set, then {@code defaultValue} is returned.
  
  @param environmentVariableName {@link String} name of the environment variable.
  @param defaultValue the default value to return if the specified environment variable is not set.
  @return the value set the environment variable identified by the given name or {@code defaultValue}
  if the named environment variable is not set.
  @see #environmentVariables()