checkExternalVariable = (variableName, request, runtimeTemplate) =>
	`if(typeof ${variableName} === 'undefined') { ${runtimeTemplate.throwMissingModuleErrorBlock(
		{ request }
	)} }\n`
@param {string} variableName the variable name to check
@param {string} request the request path
@param {RuntimeTemplate} runtimeTemplate the runtime template
@returns {string} the generated source