code: def go_unions(
      gotype: str,
      package: str,
      file: str,
      schema: Schema,
      union_spec: List[UnionSpec],
  ) -> List[str]:
      lines = []  # type: List[str]
      if len(union_spec) < 1:
          return lines
      x = gotype[0].lower()
  
      # Define a GetUnionMember() that returns an interface.
      lines.append("")
      lines.append(
          f"func ({x} {gotype}) GetUnionMember() interface{{}} {{"
      )
      for field, _ in union_spec:
          lines.append(f"\tif {x}.{field} != nil {{")
          lines.append(f"\t\treturn *{x}.{field}")
          lines.append("\t}")
      lines.append('\tpanic("no union member defined")')
      lines.append("}")
  
      return lines
  
imports: import argparse
  import json
  import os
  import re
  import sys
  from typing import List, Optional, Tuple
label_desc: Use image node_id 10 for calling a global function with example usage: go_unions(gotype, package, file, schema, union_spec) and returns: lines, lines