AWS SAM running local won't resolve FindInMap Intrinsic - aws-lambda

Question

I can't make a template.yaml with Mappings work when testing locally, although they will deploy and work as expected.
As an example, one can follow:
sam init --runtime python3.8
Insert Mappings such as the following in template.yaml
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
sam-app
Sample SAM Template for sam-app
Parameters:
Environment:
Description: 'Required. Environment'
Type: String
AllowedValues:
- test
- prod
Default: test
# More info about Globals: https://github.com/awslabs/serverless-application-model/blob/master/docs/globals.rst
Globals:
Function:
Timeout: 3
MemorySize: !FindInMap [Environments, !Ref Environment, MemorySize]
Mappings:
Environments:
test:
MemorySize: 512
prod:
MemorySize: 2048
Resources:
HelloWorldFunction:
Type: AWS::Serverless::Function # More info about Function Resource: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#awsserverlessfunction
Properties:
CodeUri: hello_world/
Handler: app.lambda_handler
Runtime: python3.8
Events:
HelloWorld:
Type: Api # More info about API Event Source: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#api
Properties:
Path: /hello
Method: get
Outputs:
# ServerlessRestApi is an implicit API created out of Events key under Serverless::Function
# Find out more about other implicit resources you can reference within SAM
# https://github.com/awslabs/serverless-application-model/blob/master/docs/internals/generated_resources.rst#api
HelloWorldApi:
Description: "API Gateway endpoint URL for Prod stage for Hello World function"
Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/hello/"
HelloWorldFunction:
Description: "Hello World Lambda Function ARN"
Value: !GetAtt HelloWorldFunction.Arn
HelloWorldFunctionIamRole:
Description: "Implicit IAM Role created for Hello World function"
Value: !GetAtt HelloWorldFunctionRole.Arn
sam build --parameter-overrides ParamaterKey=Environment,ParameterValue=test --use-container
sam local start-api --debug, and it will show unresolved references.
2021-03-06 00:30:42,394 | local start-api command is called
2021-03-06 00:30:42,399 | Collected default values for parameters: {'Environment': 'test'}
2021-03-06 00:30:42,417 | Unable to resolve property MemorySize: OrderedDict([('Fn::FindInMap', ['Environments', OrderedDict([('Ref', 'Environment')]), 'MemorySize'])]). Leaving as is.
2021-03-06 00:30:42,417 | 2 resources found in the stack
2021-03-06 00:30:42,417 | Collected default values for parameters: {'Environment': 'test'}
2021-03-06 00:30:42,433 | Unable to resolve property MemorySize: OrderedDict([('Fn::FindInMap', ['Environments', OrderedDict([('Ref', 'Environment')]), 'MemorySize'])]). Leaving as is.
2021-03-06 00:30:42,434 | Collected default values for parameters: {'Environment': 'test'}
2021-03-06 00:30:42,449 | Unable to resolve property MemorySize: OrderedDict([('Fn::FindInMap', ['Environments', OrderedDict([('Ref', 'Environment')]), 'MemorySize'])]). Leaving as is.
2021-03-06 00:30:42,449 | Found Serverless function with name='HelloWorldFunction' and CodeUri='HelloWorldFunction'
2021-03-06 00:30:42,452 | Collected default values for parameters: {'Environment': 'test'}
2021-03-06 00:30:42,467 | Unable to resolve property MemorySize: OrderedDict([('Fn::FindInMap', ['Environments', OrderedDict([('Ref', 'Environment')]), 'MemorySize'])]). Leaving as is.
2021-03-06 00:30:42,467 | 2 resources found in the template
2021-03-06 00:30:42,468 | Found '1' API Events in Serverless function with name 'HelloWorldFunction'
2021-03-06 00:30:42,468 | Detected Inline Swagger definition
2021-03-06 00:30:42,468 | Lambda function integration not found in Swagger document at path='/hello' method='get'
2021-03-06 00:30:42,468 | Found '0' APIs in resource 'ServerlessRestApi'
2021-03-06 00:30:42,468 | Removed duplicates from '0' Explicit APIs and '1' Implicit APIs to produce '1' APIs
2021-03-06 00:30:42,468 | 1 APIs found in the template
2021-03-06 00:30:42,471 | Mounting HelloWorldFunction at http://127.0.0.1:3000/hello [GET]
2021-03-06 00:30:42,471 | You can now browse to the above endpoints to invoke your functions. You do not need to restart/reload SAM CLI while working on your functions, changes will be reflected instantly/automatically. You only need to restart SAM CLI if you update your AWS SAM template
2021-03-06 00:30:42,471 | Localhost server is starting up. Multi-threading = True
2021-03-06 00:30:42 * Running on http://127.0.0.1:3000/ (Press CTRL+C to quit)
Insist with curl http://127.0.0.1/hello and sam will show an error:
2021-03-06 00:33:25,099 | Found one Lambda function with name 'HelloWorldFunction'
2021-03-06 00:33:25,099 | Invoking app.lambda_handler (python3.8)
2021-03-06 00:33:25,099 | No environment variables found for function 'HelloWorldFunction'
2021-03-06 00:33:25,099 | Environment variables overrides data is standard format
2021-03-06 00:33:25,099 | Loading AWS credentials from session with profile 'None'
2021-03-06 00:33:25,113 | Resolving code path. Cwd=/home/ricardo/Sandbox/learning/aws/sam-app/.aws-sam/build, CodeUri=/home/ricardo/Sandbox/learning/aws/sam-app/.aws-sam/build/HelloWorldFunction
2021-03-06 00:33:25,113 | Resolved absolute path to code is /home/ricardo/Sandbox/learning/aws/sam-app/.aws-sam/build/HelloWorldFunction
2021-03-06 00:33:25,113 | Code /home/ricardo/Sandbox/learning/aws/sam-app/.aws-sam/build/HelloWorldFunction is not a zip/jar file
2021-03-06 00:33:25,127 | Skip pulling image and use local one: amazon/aws-sam-cli-emulation-image-python3.8:rapid-1.19.1.
2021-03-06 00:33:25,127 | Mounting /home/ricardo/Sandbox/learning/aws/sam-app/.aws-sam/build/HelloWorldFunction as /var/task:ro,delegated inside runtime container
2021-03-06 00:33:25,127 | Cleaning all decompressed code dirs
2021-03-06 00:33:25,128 | Exception on /hello [GET]
Traceback (most recent call last):
File "/home/ricardo/.local/lib/python3.8/site-packages/docker/utils/utils.py", line 415, in parse_bytes
digits = int(digits_part)
ValueError: invalid literal for int() with base 10: "OrderedDict([('Fn::FindInMap', ['Environments', OrderedDict([('Ref', 'Environment')]), 'MemorySize'])])"
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/ricardo/.local/lib/python3.8/site-packages/flask/app.py", line 2447, in wsgi_app
response = self.full_dispatch_request()
File "/home/ricardo/.local/lib/python3.8/site-packages/flask/app.py", line 1952, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/ricardo/.local/lib/python3.8/site-packages/flask/app.py", line 1821, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/ricardo/.local/lib/python3.8/site-packages/flask/_compat.py", line 39, in reraise
raise value
File "/home/ricardo/.local/lib/python3.8/site-packages/flask/app.py", line 1950, in full_dispatch_request
rv = self.dispatch_request()
File "/home/ricardo/.local/lib/python3.8/site-packages/flask/app.py", line 1936, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/ricardo/.local/lib/python3.8/site-packages/samcli/local/apigw/local_apigw_service.py", line 297, in _request_handler
self.lambda_runner.invoke(route.function_name, event, stdout=stdout_stream_writer, stderr=self.stderr)
File "/home/ricardo/.local/lib/python3.8/site-packages/samcli/commands/local/lib/local_lambda.py", line 111, in invoke
self.local_runtime.invoke(config, event, debug_context=self.debug_context, stdout=stdout, stderr=stderr)
File "/home/ricardo/.local/lib/python3.8/site-packages/samcli/lib/telemetry/metric.py", line 216, in wrapped_func
return_value = func(*args, **kwargs)
File "/home/ricardo/.local/lib/python3.8/site-packages/samcli/local/lambdafn/runtime.py", line 148, in invoke
container = self.create(function_config, debug_context)
File "/home/ricardo/.local/lib/python3.8/site-packages/samcli/local/lambdafn/runtime.py", line 82, in create
self._container_manager.create(container)
File "/home/ricardo/.local/lib/python3.8/site-packages/samcli/local/docker/manager.py", line 95, in create
container.create()
File "/home/ricardo/.local/lib/python3.8/site-packages/samcli/local/docker/container.py", line 167, in create
real_container = self.docker_client.containers.create(self._image, **kwargs)
File "/home/ricardo/.local/lib/python3.8/site-packages/docker/models/containers.py", line 860, in create
create_kwargs = _create_container_args(kwargs)
File "/home/ricardo/.local/lib/python3.8/site-packages/docker/models/containers.py", line 1077, in _create_container_args
create_kwargs['host_config'] = HostConfig(**host_config_kwargs)
File "/home/ricardo/.local/lib/python3.8/site-packages/docker/types/containers.py", line 182, in __init__
self['Memory'] = parse_bytes(mem_limit)
File "/home/ricardo/.local/lib/python3.8/site-packages/docker/utils/utils.py", line 417, in parse_bytes
raise errors.DockerException(
docker.errors.DockerException: Failed converting the string value for memory (OrderedDict([('Fn::FindInMap', ['Environments', OrderedDict([('Ref', 'Environment')]), 'MemorySize'])])) to an integer.
sam --version gives SAM CLI, version 1.19.1.
Isn't FindInMap intrinsic still not implemented? What am I doing wrong?