AttributeError in intrinsics_symbol_table.py

### Description

Trying to run the command `sam local start-api` and get an error.

### Observed result

```
Traceback (most recent call last):
File "/usr/local/bin/sam", line 11, in
load_entry_point('aws-sam-cli==0.21.0', 'console_scripts', 'sam')()
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 764, in __call__
return self.main(*args, **kwargs)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 717, in main
rv = self.invoke(ctx)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 956, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 555, in invoke
return callback(*args, **kwargs)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/decorators.py", line 64, in new_func
return ctx.invoke(f, obj, *args, **kwargs)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 555, in invoke
return callback(*args, **kwargs)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/telemetry/metrics.py", line 51, in wrapped
return func(*args, **kwargs)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/start_api/cli.py", line 60, in cli
parameter_overrides) # pragma: no cover
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/start_api/cli.py", line 90, in do_cli
aws_profile=ctx.profile) as invoke_context:
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/cli_common/invoke_context.py", line 133, in __enter__
self._function_provider = SamFunctionProvider(self._template_dict, self.parameter_overrides)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/lib/sam_function_provider.py", line 46, in __init__
self.template_dict = SamBaseProvider.get_template(template_dict, parameter_overrides)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/lib/sam_base_provider.py", line 53, in get_template
template_dict = resolver.resolve_template(ignore_errors=True)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 240, in resolve_template
processed_template["Resources"] = self.resolve_attribute(self._resources, ignore_errors)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 265, in resolve_attribute
processed_resource = self.intrinsic_property_resolver(val, parent_function=processed_key)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 220, in intrinsic_property_resolver
sanitized_val = self.intrinsic_property_resolver(val, parent_function=parent_function)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 220, in intrinsic_property_resolver
sanitized_val = self.intrinsic_property_resolver(val, parent_function=parent_function)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 199, in intrinsic_property_resolver
return [self.intrinsic_property_resolver(item) for item in intrinsic]
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 199, in
return [self.intrinsic_property_resolver(item) for item in intrinsic]
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 220, in intrinsic_property_resolver
sanitized_val = self.intrinsic_property_resolver(val, parent_function=parent_function)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 220, in intrinsic_property_resolver
sanitized_val = self.intrinsic_property_resolver(val, parent_function=parent_function)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 199, in intrinsic_property_resolver
return [self.intrinsic_property_resolver(item) for item in intrinsic]
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 199, in
return [self.intrinsic_property_resolver(item) for item in intrinsic]
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 220, in intrinsic_property_resolver
sanitized_val = self.intrinsic_property_resolver(val, parent_function=parent_function)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 199, in intrinsic_property_resolver
return [self.intrinsic_property_resolver(item) for item in intrinsic]
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 199, in
return [self.intrinsic_property_resolver(item) for item in intrinsic]
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 213, in intrinsic_property_resolver
return self.conditional_key_function_map.get(key)(intrinsic_value)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 753, in handle_fn_if
intrinsic_value, parent_function=IntrinsicResolver.FN_IF
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 199, in intrinsic_property_resolver
return [self.intrinsic_property_resolver(item) for item in intrinsic]
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 199, in
return [self.intrinsic_property_resolver(item) for item in intrinsic]
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 210, in intrinsic_property_resolver
return self.intrinsic_key_function_map.get(key)(intrinsic_value)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py", line 659, in handle_fn_ref
return self._symbol_resolver.resolve_symbols(arguments, IntrinsicResolver.REF)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsics_symbol_table.py", line 217, in resolve_symbols
translated = self.get_translation(logical_id, resource_attribute)
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/intrinsic_resolver/intrinsics_symbol_table.py", line 323, in get_translation
return logical_id_item.get(resource_attributes)
AttributeError: 'NoneType' object has no attribute 'get'
```
### Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. OS: OSX 10.14.6
2. `sam --version`: SAM CLI, version 0.21.0
3. AWS CLI: aws-cli/1.16.230 Python/3.7.4 Darwin/18.7.0 botocore/1.12.220
4. Node: v10.16.3