KtFile: SimpleFunctionWithContract.kt
  PACKAGE_DIRECTIVE
    <empty list>
  IMPORT_LIST
    <empty list>
  FUN
    PsiElement(fun)('fun')
    PsiWhiteSpace(' ')
    PsiElement(IDENTIFIER)('foo')
    VALUE_PARAMETER_LIST
      PsiElement(LPAR)('(')
      VALUE_PARAMETER
        PsiElement(IDENTIFIER)('s')
        PsiElement(COLON)(':')
        PsiWhiteSpace(' ')
        TYPE_REFERENCE
          NULLABLE_TYPE
            USER_TYPE
              REFERENCE_EXPRESSION
                PsiElement(IDENTIFIER)('String')
            PsiElement(QUEST)('?')
      PsiElement(RPAR)(')')
    PsiWhiteSpace(' ')
    PsiElement(contract)('contract')
    PsiWhiteSpace(' ')
    CONTRACT_EFFECT_LIST
      PsiElement(LBRACKET)('[')
      CONTRACT_EFFECT
        BINARY_EXPRESSION
          CALL_EXPRESSION
            REFERENCE_EXPRESSION
              PsiElement(IDENTIFIER)('returns')
            VALUE_ARGUMENT_LIST
              PsiElement(LPAR)('(')
              PsiElement(RPAR)(')')
          PsiWhiteSpace(' ')
          OPERATION_REFERENCE
            PsiElement(IDENTIFIER)('implies')
          PsiWhiteSpace(' ')
          PARENTHESIZED
            PsiElement(LPAR)('(')
            BINARY_EXPRESSION
              REFERENCE_EXPRESSION
                PsiElement(IDENTIFIER)('s')
              PsiWhiteSpace(' ')
              OPERATION_REFERENCE
                PsiElement(EXCLEQ)('!=')
              PsiWhiteSpace(' ')
              NULL
                PsiElement(null)('null')
            PsiElement(RPAR)(')')
      PsiElement(RBRACKET)(']')
    PsiWhiteSpace(' ')
    BLOCK
      PsiElement(LBRACE)('{')
      PsiWhiteSpace('\n    ')
      BINARY_EXPRESSION
        REFERENCE_EXPRESSION
          PsiElement(IDENTIFIER)('s')
        PsiWhiteSpace(' ')
        OPERATION_REFERENCE
          PsiElement(ELVIS)('?:')
        PsiWhiteSpace(' ')
        THROW
          PsiElement(throw)('throw')
          PsiWhiteSpace(' ')
          CALL_EXPRESSION
            REFERENCE_EXPRESSION
              PsiElement(IDENTIFIER)('NullArgumentException')
            VALUE_ARGUMENT_LIST
              PsiElement(LPAR)('(')
              PsiElement(RPAR)(')')
      PsiWhiteSpace('\n')
      PsiElement(RBRACE)('}')