[typescript-angular] Generated APIs contain errors (angular 7.2.0)

Description

The code for the generated API services contain TSLINT errors and a comiplation error.

The generated code has a lot of the following:

• let httpHeaderAccepts: string[] should be const httpHeaderAccepts: string[] since its not modified afterwards.

• if (httpHeaderAcceptSelected != undefined) { headers = headers.set('Accept', httpHeaderAcceptSelected); } should be if (httpHeaderAcceptSelected !== undefined) { headers = headers.set('Accept', httpHeaderAcceptSelected); }

• if (httpContentTypeSelected != undefined) { headers = headers.set('Content-Type', httpContentTypeSelected); } should be if (httpContentTypeSelected !== undefined) { headers = headers.set('Content-Type', httpContentTypeSelected); }

• return this.httpClient.post<any>(${this.basePath}/pet, body, { withCredentials: this.configuration.withCredentials, headers: headers, observe: observe, reportProgress: reportProgress } ); don't know why but it keeps givving me the following error on headers, observe and reportProgress: TSLint: Expected property shorthand in object literal ('{reportProgress}'). (object-literal-shorthand)

• And finally the compilation error: formParams = formParams.append('name', <any>name) || formParams; Error: ERROR in ../pet.service.ts(451,26): error TS1345: An expression of type 'void' cannot be tested for truthiness

Swagger-codegen version

2.4.2

Swagger declaration file content or url

The standard pet store swagger file used in all their examples.
https://petstore.swagger.io/v2/swagger.json

Command line used for generation

<plugin> <groupId>io.swagger</groupId> <artifactId>swagger-codegen-maven-plugin</artifactId> <version>2.4.2</version> <executions> <execution> <goals> <goal>generate</goal> </goals> <configuration> <inputSpec>${swaggerContractsDirectory}/swagger.json</inputSpec> <language>typescript-angular</language> <output>${swaggerOutputDirectory}</output> <configOptions> <ngVersion>7.2.0</ngVersion> <providedInRoot>true</providedInRoot> </configOptions> <generateApiTests>false</generateApiTests> <generateApiDocumentation>false</generateApiDocumentation> <generateModelTests>false</generateModelTests> <generateModelDocumentation>false</generateModelDocumentation> <supportingFilesToGenerate>variables.ts,configuration.ts,encoder.ts</supportingFilesToGenerate> <!--<generateSupportingFiles>false</generateSupportingFiles>--> </configuration> </execution> </executions> </plugin>

Steps to reproduce

Execute a mvn clean install on the pom containing the code above

Start by reproducing the generated TypeScript Angular client from the standard Pet Store Swagger file using the Maven configuration in the issue, then inspect the typescript-angular generator output responsible for the generated API services. Done means the generated services compile under Angular 7.2.0 and no longer produce the reported TSLint errors.