title: Error encountered in metadata generated for exported symbol when constructing an angular 6 library
body: <p>I'm getting the following error while performing 'ng build' from my library.</p>
  
  <p>I'm using Angular 6 at the moment, but I believe this error is not version related.</p>
  
  <blockquote>
    <p>/home/rafaelvicio/desenv/my-lib/arquitetura-web/projects/pf-siseg/src/lib/keycloak-service/keycloak.service.ts:13:1:
    Error encountered in metadata generated for exported symbol
    'KeycloakService':<br>
    /home/rafaelvicio/desenv/my-lib/arquitetura-web/projects/pf-siseg/src/lib/keycloak-service/keycloak.service.ts:18:12:
    Metadata collected contains an error that will be reported at runtime:
    Only initialized variables and constants can be referenced because the
    value of this variable is needed by the template compiler.<br>
    {"__symbolic":"error","message":"Variable not
    initialized","line":17,"character":11} Error:
    /home/rafaelvicio/desenv/my-lib/arquitetura-web/projects/pf-siseg/src/lib/keycloak-service/keycloak.service.ts:13:1:
    Error encountered in metadata generated for exported symbol
    'KeycloakService':<br>
    /home/rafaelvicio/desenv/my-lib/arquitetura-web/projects/pf-siseg/src/lib/keycloak-service/keycloak.service.ts:18:12:
    Metadata collected contains an error that will be reported at runtime:
    Only initialized variables and constants can be referenced because the
    value of this variable is needed by the template compiler.<br>
    {"__symbolic":"error","message":"Variable not
    initialized","line":17,"character":11}
        at /home/rafaelvicio/desenv/my-lib/arquitetura-web/node_modules/@angular/compiler-cli/src/metadata/collector.js:707:31
        at Array.forEach ()
        at validateMetadata (/home/rafaelvicio/desenv/my-lib/arquitetura-web/node_modules/@angular/compiler-cli/src/metadata/collector.js:695:46)
        at MetadataCollector.getMetadata (/home/rafaelvicio/desenv/my-lib/arquitetura-web/node_modules/@angular/compiler-cli/src/metadata/collector.js:550:21)
        at MetadataCache.getMetadata (/home/rafaelvicio/desenv/my-lib/arquitetura-web/node_modules/@angular/compiler-cli/src/transformers/metadata_cache.js:86:41)
        at Object.getSourceFileMetadata (/home/rafaelvicio/desenv/my-lib/arquitetura-web/node_modules/@angular/compiler-cli/src/transformers/compiler_host.js:112:56)
        at Object.readMetadata (/home/rafaelvicio/desenv/my-lib/arquitetura-web/node_modules/@angular/compiler-cli/src/transformers/metadata_reader.js:46:37)
        at TsCompilerAotCompilerTypeCheckHostAdapter.getMetadataFor (/home/rafaelvicio/desenv/my-lib/arquitetura-web/node_modules/@angular/compiler-cli/src/transformers/compiler_host.js:464:38)
        at StaticSymbolResolver.getModuleMetadata (/home/rafaelvicio/desenv/my-lib/arquitetura-web/node_modules/@angular/compiler/src/aot/static_symbol_resolver.js:480:49)
        at StaticSymbolResolver._createSymbolsOf (/home/rafaelvicio/desenv/my-lib/arquitetura-web/node_modules/@angular/compiler/src/aot/static_symbol_resolver.js:268:33)</p>
  </blockquote>
  
  <p>keycloak.service.ts:</p>
  
  <pre><code>import { Injectable } from '@angular/core';
  import { KeycloakLoginOptions } from './keycloak.d';
  
  import { HttpClient } from '@angular/common/http';
  import { Observable } from 'rxjs/Observable';
  
  import * as Keycloak from './keycloak';
  
  export type KeycloakClient = Keycloak.KeycloakInstance;
  type InitOptions = Keycloak.KeycloakInitOptions;
  
  @Injectable()
  export class KeycloakService {
  
      constructor(private http: HttpClient) { }
  
      static keycloakAuth: KeycloakClient;
  
  .... More code here
  </code></pre>