title: glue maps not returning record when using isdigit() function in glue map transform
body: <p>I am trying to call a map. apply to transform on dynamic frames in AWS glue which will create a new column in the dynamic frame and populates its value based on whether my other column is a digit or not.</p>
  
  <p>I have created a data frame and converted it into a dynamic frame and then call map. apply. I have created a python definition which will check whether the column is a digit or not and passed it to map.apply.But after applying this map rec is returning null.</p>
  
  <pre><code>def isDigit(rec):
      if rec["_4"]:
          rec["hey"] =1
      return rec
  
  l = [('1','125','REF123','1.5','Normal','Diagonose','12 12 2018'),('2','124','REF1234','1.7','Critical','Report','14 Mar 2019'),
      ('3',None,'REF1234','1.8','Critical','Report','12 Jan 2018')]
  source_file = sc.parallelize(l)
  
  source_file = source_file.toDF()
  source_file  = DynamicFrame.fromDF(source_file, glueContext, "datasource1")
  mapped_dyF = Map.apply(frame = source_file, f = isDigit)
  mapped_dyF.toDF().show()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/bsixo.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bsixo.png" alt="enter image description here"></a></p>
  
  <p>Above code worked fine but while I am using isDigit() its no records in returned </p>
  
  <pre><code>While using isDigit() it reuturn null 
  def isDigit(rec):
      **if rec["_4"].isDigit():**
          rec["hey"] =1
      return rec
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/shh6J.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/shh6J.png" alt="enter image description here"></a></p>
  
  <p>I want to get the value of 1 in hey column if column _4 is a digit.</p>