Correctly encode plus sign in parameters

Fixes #20

templates/baseService.mustache

@@ -1,7 +1,30 @@
 /* tslint:disable */
-import { HttpClient } from '@angular/common/http';
+import { HttpClient, HttpParameterCodec, HttpParams } from '@angular/common/http';
 import { ApiConfiguration } from './api-configuration';
 
+/**
+ * Custom parameter codec to correctly handle the plus sign in parameter
+ * values. See https://github.com/angular/angular/issues/18261
+ */
+class ParameterCodec implements HttpParameterCodec {
+  encodeKey(key: string): string {
+    return encodeURIComponent(key);
+  }
+
+  encodeValue(value: string): string {
+    return encodeURIComponent(value);
+  }
+
+  decodeKey(key: string): string {
+    return decodeURIComponent(key);
+  }
+
+  decodeValue(value: string): string {
+    return decodeURIComponent(value);
+  }
+}
+const PARAMETER_CODEC = new ParameterCodec();
+
 /**
  * Base class for API services
  */
@@ -28,4 +51,13 @@ export class BaseService {
   set rootUrl(rootUrl: string) {
     this._rootUrl = rootUrl;
   }
+
+  /**
+   * Creates a new `HttpParams` with the correct codec
+   */
+  protected newParams(): HttpParams {
+    return new HttpParams({
+      encoder: PARAMETER_CODEC
+    });
+  }
 }

templates/operationResponse.mustache

@@ -6,7 +6,7 @@
   }}{{^paramIsLast}},
     {{/paramIsLast}}{{/operationParameters}}{{/operationParamsClass
     }}): Observable<HttpResponse<{{operationResultType}}>> {
-    let __params = new HttpParams();
+    let __params = this.newParams();
     let __headers = new HttpHeaders();
     let __body: any = null;
 {{#operationParameters}}{{>parameter}}