title: Issues using mergeDynamicFrame on AWS Glue
body: <p>I need do a merge between two dynamic frames on Glue.
  I tried to use the mergeDynamicFrame function, but i keep getting the same error:</p>
  <p>AnalysisException: &quot;cannot resolve '<code>id</code>' given input columns: [];;\n'Project ['id]\n+- LogicalRDD false\n&quot;</p>
  <p>Right now, i have 2 DF:
  df_1(id, col1, salary_src) and df_2(id, name, salary)</p>
  <p>I want to merge df_2 into df_1 by the &quot;id&quot; column.</p>
  <pre><code>df_1 = glueContext.create_dynamic_frame.from_catalog(......)
  df_2 = glueContext.create_dynamic_frame.from_catalog(....)
  
  merged_frame = df_1.mergeDynamicFrame(df_2, [&quot;id&quot;]) 
  
  applymapping1 = ApplyMapping.apply(frame = merged_frame, mappings = [(&quot;id&quot;, &quot;long&quot;, &quot;id&quot;, &quot;long&quot;), (&quot;col1&quot;, &quot;string&quot;, &quot;name&quot;, &quot;string&quot;), (&quot;salary_src&quot;, &quot;long&quot;, &quot;salary&quot;, &quot;long&quot;)], transformation_ctx = &quot;applymapping1&quot;)
  
  datasink2 = glueContext.write_dynamic_frame.from_options(....)
  </code></pre>
  <p>As a test i tried to pass a column from both DFs (salary and salary_src), and, the error as:</p>
  <p>AnalysisException: &quot;cannot resolve '<code>salary_src</code>' given input columns: [id, name, salary];;\n'Project [salary#2, 'salary_src]\n+- LogicalRDD [id#0, name#1, salary#2], false\n&quot;</p>
  <p>Is this case, it seems to recognize the columns from the df_2 (id, name, salary).. but if i pass just one of the columns, or even the 3, it keeps failing</p>