title: Syntax while setting schema for Pyspark.sql using StructType
body: <p>I am new to spark and was playing around with Pyspark.sql. According to the pyspark.sql documentation <a href="https://spark.apache.org/docs/latest/api/python/pyspark.sql.html#" rel="noreferrer">here</a>, one can go about setting the Spark dataframe and schema like this:</p>
  <pre><code>spark= SparkSession.builder.getOrCreate()
  from pyspark.sql.types import StringType, IntegerType, 
  StructType, StructField
  
  rdd = sc.textFile('./some csv_to_play_around.csv'
  
  schema = StructType([StructField('Name', StringType(), True),
                       StructField('DateTime', TimestampType(), True)
                       StructField('Age', IntegerType(), True)])
  
  # create dataframe
  df3 = sqlContext.createDataFrame(rdd, schema)
  </code></pre>
  <p>My question is, what does the <code>True</code> stand for in the <code>schema</code> list above? I can't seem to find it in the documentation. Thanks in advance</p>