class GraphQL::ObjectType::UnresolvedTypeError

for the field.
Error raised when the value provided for a field can’t be resolved to one of the possible types

def exception_message 

def exception_message
  "The value returned for field #{field_name} on #{parent_type} could not be resolved "\
  "to one of the possible types for #{field_type}."
end

def initialize(field_name, field_type, parent_type) 

def initialize(field_name, field_type, parent_type)
  @field_name = field_name
  @field_type = field_type
  @parent_type = parent_type
  super(exception_message)
end